Desiccant comprising nanofibers

Abstract

The present invention relates to a process to remove water from a gas by contacting the gas with a desiccant comprising nanofibers of a cross-linked hydrophilic polymer. wherein the cross-linked hydrophilic polymer is selected from the list comprising: Poly(2- alkyl-2-oxazoline) (PEOx), Poly(acrylic acid) (PAA), Polyethylene glycol (PEG), Polyhydroxyethylmethacrylate (PHEMA), Poly(N-vinyl imidazole) (PVIM), Poly[2 (Dimethylamino)ethyl Methacrylate] (PDMAEMA), Polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), pullulan, chitosan, keratine, gelatin, salts, derivatives and copolymers thereof.

Description

[0001] DESICCANT COMPRISING NANOFIBERS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a desiccant for the sorption of water. The desiccant of the present invention can be regenerated easily at low temperature and provides better water adsorption efficiency at low relative humidity.

[0004] BACKGROUND TO THE INVENTION

[0005] In households, moisture is generated daily through a variety of sources (cooking, cleaning, bathing and, more). The removal of excess moisture is done usually for health or comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting water from the air. Excess moisture is well known to cause mold and fungal growth. Mold growth is often accompanied by unpleasant odors that release Microbial Volatile Organic Compounds (mVOC) during reproduction. Exposure to mVOC’s can lead to headaches, nasal irritation, dizziness, fatigue, nausea, respiratory infections, and Toxic Mold Syndrome. Further, excess moisture in households due to high levels of humidity can quickly cause damage to property. Condensation forming on windows can quickly lead to discoloration, staining, peeling wallpaper, and blistering paint.

[0006] Legislation around the world require newly constructed buildings to meet stricter and stricter energy efficiency standards, sometimes leading house planners to choose for tighter spaces, which might be insufficiently ventilated. Unfortunately, insufficient ventilation will lead to moisture problems, musty odors, high levels of pollutants, structural damage, potential litigation, and more. There is therefore an increasing need for dehumidifier installations and moisture absorbing materials, meeting energy efficiency standards.

[0007] Indoor, a relative humidity (RH) between 40% and 60% is favorable. Currently, there are several ways for air dehumidification. Most household air conditioners dehumidify air by the refrigerant cooling method. That is, the air is first cooled below the dew-point temperature to condense the moisture out, and then reheated to the required condition. Obviously, both cooling and heating processes consume huge amounts of energy.

[0008] US6143390A discloses a low-temperature regenerative type moisture absorbing material comprising fibers for dehumidifying and drying, and a dehum idifying-and-drying device comprising said absorbing material shaped to form plural gas passages. The fibers in said absorbing material are of a polymeric compound containing a salt having carboxylic groups and crosslinked by hydrazine or a derivative thereof. The moisture absorbing material disclosed in US6143390A have high moisture absorbing and releasing properties, with the regeneration temperature of about 70 °C. The absorbing material disclosed in US6143390A has several drawbacks, first, the materials do not provide efficient water adsorption for low relative humidity (RH), second the materials described in US6143390A are complex and limited to those comprising carboxyl moieties, and third, their synthesis requires the use of hydrazine and derivatives, known to raise safety concerns due to their toxicity, and it is limited to crosslinked materials. Further, absorbing materials described in US6143390A can be efficiently regenerated only at relatively high temperatures. Absorbing material described in US6143390A are therefore poorly suitable for use in household environments, and especially in energy efficient dehumidifying-and-drying devices.

[0009] In Dai Li et al., ‘Sorption and regeneration performance of novel solid desiccant based on PVA-LiCI electrospun nanofibrous membrane, Polymer Testing 64 (2017) 242-249, non-cross-linked nanofibrous membranes are described containing polyvinyl alcohol (PVA)- LiCI which are used as desiccants. Sorption is caried out at 25 C at 80% relative humidity (RH) and desorption at 50 C at 26% RH. The LiCI is said to increase the sorption capacity of the PVA significantly because the LiCI increases the hygroscopicity of the PVA leading to a larger driving force for water diffusion according to this article. At higher contents of LiCI a higher capacity is achieved. A problem with the use of salts like LiCI, Li Br and CaCl2 is their so-called carryout problem as mentioned in this article. This could results in unwanted corrosion problems in the used equipment. The article does refer to MOF type materials which are used as desiccants in the absence of such a salt. MOF type materials however are less stable and its structure is easily destroyed during the regeneration process according to the same article. The article further states that hydrophilic polymer materials are known for their good absorption capacity, but poor absorption kinetics.

[0010] Yao Ye et al., "Photo-crosslinked nanofibrous membranes as advanced low-temperature regenerative desiccant", Polymer Testing 78 (2019) 105947 describes a polyamide 6 and LiCI containing membrane as a low-temperature regenerative desiccant.

[0011] Y. Li, M. Vergaelen, E. Schoolaert, R. Hoogenboom, and K. De Clerck, d, Eur. Polym. J., vol. 112, no. November 2018, pp. 24-30, Mar. 2019 describes the effect of crosslinking stage on photocrosslinking of benzophenone functionalized poly(2-ethyl-2-oxazoline) nanofibers obtained by aqueous electrospinning. These PEtOx-BP cross-linked nanofibres are hydrophilic.

[0012] Therefore, there is a need for stable absorbing materials which do not require a salt, like the above referred to salts and especially LiCI, which can be easily regenerated and have a good water absorption capacity and absorption kinetics.

[0013] SUMMARY OF THE INVENTION

[0014] The above aim is achieved by the following process. A process to remove water from a gas by contacting the gas with a desiccant comprising nanofibers of a cross-linked hydrophilic polymer. Applicants found that the desiccant used in the process is a stable absorbing material which does not require LiCI and provides a good water absorption efficiency and good absorption kinetics. An advantage of the present invention is that the desiccant provides for a larger surface area, which translates into much higher sorption capacity. Further, desiccants according to the present invention provide higher adsorption rates compared to desiccants in powder or film form. The hydrophilic polymer allows for easy regenerating by a mild temperature increase because the polymer becomes less hydrophilic upon heating

[0015] According to an embodiment of the present invention, the hydrophilic polymer is a polymer providing a weight change (%), which is a weight gain, upon contact with water vapor at 90% relative humidity (RH) of at least 20%, preferably at least 30%, preferably at least 40%. It has been found that the use of hydrophilic polymers providing a weight change (%) according to the present embodiment is beneficial in achieving higher adsorption rates.

[0016] According to a further embodiment of the present invention, the nanofibers have an average fiber diameter from about 100 nm to about 3000 nm, preferably the nanofibers have an average fiber diameter from 200 nm to 1000 nm, more preferably the average diameter of the nanofibers is from about 400 nm to about 800 nm. The average diameter is measured by scanning electron microscopy. It has been found particularly advantageous to provide for desiccants comprising nanofibers according to the present embodiment, as higher adsorption rates can be achieved.

[0017] According to a further embodiment of the present invention, the polymer is a crosslinked polymer. By means of crosslinking the nanofibers, the nanofibrous desiccant according to the present invention is more morphologically stable after several sorption-desorption cycles.

[0018] According to a further embodiment of the present invention, wherein the polymer is selected from the list comprising: Poly(2- alkyl-2-oxazoline) (PEOx), Poly(acrylic acid) (PAA), Polyethylene glycol (PEG), Polyhydroxyethylmethacrylate (PHEMA), Poly(N-vinyl imidazole) (PVIM), Poly[2 (Dimethylamino)ethyl Methacrylate] (PDMAEMA), Polyvinylpyrrolidone (PVP), poly(vinl alcohol) (PVA), pullulan, chitosan, keratine, gelatin, salts, derivatives and copolymers thereof. An advantage of the present embodiment is that using such hydrophilic polymers enhances the water sorption rate and the water sorption capacity.

[0019] According to a further embodiment of the present invention, the polymer is a Poly(2- alkyl-2-oxazoline). Preferably, the Poly(2- alkyl-2-oxazoline) is selected from the list comprising: Poly(2- ethyl-2-oxazoline) (PEtOx), Poly(2- methyl-2-oxazoline) (PMeOx), preferably Poly(2-methyl-2-oxazoline). An advantage of the present embodiment is that these are non-ionic hydrophilic polymers that are easily processed into nanofibrous materials.

[0020] In a second aspect, the present invention pertains to the use of a desiccant according to any one of the previous claims for the sorption of water vapor.

[0021] According to an embodiment of the present invention, the use of the desiccant is at a relative humidity (RH) lower than 40%, preferably lower than 30%, preferably lower than 20%, preferably lower than 10%.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] With specific reference now to the figures, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the different embodiments of the present invention only. They are presented in the cause of providing what is believed to be the most useful and readily description of the principles and conceptual aspects of the invention. In this regard no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0024] Figure 1 , also abbreviated as Fig. 1, illustrates the moisture sorption kinetics of both PEtOx nanofibers (% weight change peak to the left) and PEtOx powder (% weight change peak to the right).

[0025] Figure 2, also abbreviated as Fig. 2, illustrates the adsorption rate for each adsorption step of both AQ200 nanofibers (black) and AQ200 powder (white).

[0026] Figure 3, also abbreviated as Fig. 3, illustrates the moisture sorption kinetics of AQ50 film and AQ50 powder (referenced with arrows on the plot) and three AQ50 nanofibrous membranes with a varying fiber diameter; 210 ± 85 nm (solid line), 575 ± 103 nm (dashed line) and 2967 ± 275 nm (dash - dot line).

[0027] Figure 4, also abbreviated as Fig. 4, illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of (from left to right respectively for each RH Change range) AQ50 powder, AQ50 film, and three AQ50 nanofibrous membranes with a varying fiber diameter; 210 ± 85 nm, 575 ± 103 nm and 2967 ± 275 nm.

[0028] Figure 5, also abbreviated as Fig. 5, illustrates the moisture sorption kinetics during multiple sorption / desorption cycles of two PEtOx-PEI-CC crosslinked nanofibrous membranes with a varying fiber diameter; 456 ± 75 nm (black) and 659 ± 105 nm (light grey).

[0029] Figure 6, also abbreviated as Fig. 6, illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of two PEtOx-PEI-CC cross-linked nanofibrous membranes with a varying fiber diameter; 456 ± 75 nm (black) and 659 ± 105 nm (white).

[0030] Figure 7, also abbreviated as Fig. 7, illustrates the moisture sorption kinetics during multiple sorption / desorption cycles of four cross-linked PEtOx- PEI-BP nanofibrous membranes with a varying fiber diameter and duration of crosslinking; 475 ± 93 nm and 45 min UV, 321 ± 64 nm and 40 min UV, 787 ± 108 nm and 60 min UV and 783 ± 95 nm and 90 min UV.

[0031] Figure 8A an B, also abbreviated as Fig. 8A and B, illustrate the adsorption rate for each adsorption step of the first imposed adsorption cycle of four cross-linked PEtOx-PEI-BP nanofibrous membranes with a varying fiber diameter and duration of crosslinking (respectively, from left to right, for each RH Change range), 321 ± 64 nm and 40 min UV, 475 ± 93 nm and 45 min UV, 787 ± 108 nm and 60 min UV and 738 ± 95 nm and 90 min UV.

[0032] Figure 9, also abbreviated as Fig. 9, illustrates the moisture sorption kinetics of PVP K90 film and four PVP K90 nanofibrous membranes with a varying fiber diameter; 280 ± 48 nm (solid line), 318 ± 54 nm (dashed line), 482 ± 71 nm (long-dash-dash line) and 947 ± 145 nm (long-long line).

[0033] Figure 10, also abbreviated as Fig. 10, illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of (from left to right respectively for each RH Change range) PVP K90 film, and four PVP K90 nanofibrous membranes with a varying fiber diameter; 280 ± 48 nm, 318 ± 54 nm, 482 ± 71 nm and 947 ± 145 nm.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will now be further described. In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. When describing the compounds of the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0036] The term "about" or "approximately" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / - 10 % or less, preferably + / - 5 % or less, more preferably + / - 1 % or less, and still more preferably + / - 0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention. It is to be understood that the value to which the modifier "about" or "approximately" refers is itself also specifically, and preferably, disclosed.

[0037] As used in the specification and the appended claims, the singular forms 'a", "an", and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a nanofiber" means one nanofiber or more than one nanofiber.

[0038] An advantage of the present invention is that nanofibers provide a much higher contact area and hence much faster moisture sorption and desorption. As a result of the very fast water uptake and release of the nanofiber system, the adsorption and regeneration cycles can be much shorter allowing the development of much smaller dehumidifiers that operate at low energy consumption as the regeneration is related to the polymer phase transition rather than the boiling of water. Further, it has been surprisingly found that desiccants according to the present invention are particularly beneficial in not only increasing the adsorption and desorption rate in general, but more in particular improves the moisture adsorption rate at low relative humidity. A further advantage of the desiccant of the present invention is that it requires relatively low desorption temperatures in order to regenerate itself. A final unexpected observation is that the adsorption rate and desorption rate do not scale linearly with the surface area of the nanofibers, which would lead to an expected continuous increase of sorption / desorption rates with decreasing nanofiber diameter. Instead, we unexpectedly found that an optimal intermediate fiber diameter exists that shows the highest sorption / desorption rates.

[0039] The nanofibers as defined according to the present invention are capable of sorbing water vapor from the air and other gases, thereby swelling. The moisture uptake of the desiccant of the present invention is made possible by means of the hydrophilic polymer said nanofibers are made of.

[0040] In the context of the present invention, by means of the term “desiccant”, reference is made to a material which absorbs or adsorbs moisture from the air, causing a state of dryness (desiccation) in its vicinity. In other words, reference is made to a material that has a high affinity for water and can be used as a drying agent. Although technically different in the mechanism of reaction, for the purposes of this invention, the terms absorbing and adsorbing are intended to be used interchangeably and are referred to by the term “sorbing”.

[0041] The process according to the present invention may be used in any application in which sorption of moisture is desirable. Non-limiting examples include packaging of goods that are sensitive to moisture, such as chemicals, diagnostics, pharmaceuticals, food, spices and herbs other nutritional products and water sensitive technical products such as semiconductors or any general application that makes use of confined spaces in which a low humidity level is required over a period of time. This includes, without limitation, primary and secondary packaging. Further, the process according to the present invention may be used in dehumidification processes and for air conditioning processes to sorb moisture. Yet another application could be water-harvesting or waterretention from the air, in which the low temperature regeneration could lead to collection of water or slow release of the sorbed water.

[0042] In the context of the present invention, by means of the term “hydrophilic polymer”, reference is made to a polymer which dissolves in or is swollen by, water. Many compounds of major technical and economic importance fall within this definition, including many polymers of natural origin. Hydrophilic polymers are characterized by the presence of polar groups attached to the main polymer backbone of the molecule, such as hydroxyl (-OH), carboxyl (-COOH) and amino (-NH2) groups. The hydrophilic polymer according to the present invention may be selected form the list comprising, and are not limited to: Poly(acrylamide), Poly(2-acrylamido-2-methylpropane sulfonic acid), Poly(N,N-diethyl acrylamide), Poly(N-isopropyl acrylamide), Poly(N,N-dimethyl acrylamide), Poly(N,N-dimethylaminopropyl acrylamide), Poly(N-phenethyl methacrylamide), Poly(acrylic acid) (PAA), Poly(a-ethylacrylic acid), Poly(methacrylic acid), Poly(a-propylacrylic acid), Poly(2-aminoethyl methacrylate), Poly(2- hydroxyethyl methacrylate) (PHEMA), Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), Polyethylene glycol) (PEG), Poly(ethylene glycol) benzyl ether, Poly(ethylene glycol) decyl ether, Poly(ethylene glycol) ethyl ether, Poly(ethylene glycol) dimethyl ether, Poly(ethylene glycol) methyl ether, Poly(4- styrene sulfonic acid), Poly(N-vinyl acetamide), Poly(N-vinyl formamide), Poly(N-vinyl isobutyramide), Poly(vinylamine), Poly(N-vinyl pyrrolidone) (PVP), Poly(2-vinyl pyrazine), Poly(N-vinyl imidazole) (PVIM), Poly(2-vinyl pyridine), Poly(4-vinyl pyridine), poly(vinyl alcohol) (PVA), Poly(ethylene imine), Poly(2- alkyl-2-oxazoline) (PEOx), Poly(L-histidine), Poly(methyl vinyl ether), Poly(oxymethylene), Poly(L-proline), Poly(tetrahydrofuran), salts, polysaccharides, such as pullulan and chitosan, polyamino acids, polypeptides, proteins, such as keratine and gelatin, derivatives and copolymers thereof.

[0043] According to a further embodiment of the present invention, wherein the polymer is selected from the list comprising: Poly(2- alkyl-2-oxazoline) (PEOx), Poly(acrylic acid) (PAA), Polyethylene glycol (PEG), Polyhydroxyethylmethacrylate (PHEMA), Poly(N-vinyl imidazole) (PVIM), Poly[2 (Dimethylamino)ethyl Methacrylate] (PDMAEMA), Polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), salts, derivatives and copolymers thereof.

[0044] According to a further embodiment of the present invention, the polymer is a Poly(2- alkyl-2-oxazoline). Preferably, the Poly(2- alkyl-2-oxazoline) is selected from the list comprising: Poly(2- ethyl-2-oxazoline) (PEtOx), Poly(2- methyl-2-oxazoline) (PMeOx), preferably Poly(2-methyl-2-oxazoline).

[0045] The polymer is preferably a thermoresponsive polymer. An advantage of the present embodiment is that the thermoresponsive polymers enables energy-efficient regeneration of the desiccant by mild heating. Thermoresponsive polymers are categorized in two categories depending on whether they exhibit a lower critical solution temperature (LCST) or an upper critical solution temperature (LICST). Both classes comprise polymers that change their physicochemical properties above a certain temperature. LICST polymers are non-soluble at low temperatures and become soluble above the LICST by an enthalpic-driven process. Conversely, LCST-type polymers interact well with their solvent at low temperatures but undergo sharp coil-to-globule transition at or above their LCST and drop out of solution by an entropy increase. Both mechanisms are rooted to the so-called hydrophobic effect of water and can be described as binary systems composed of the solvent (or a mixture of solvents) and the polymer, with their mixability being dependent by temperature and the polymer fraction.

[0046] According to an embodiment of the present invention, the polymer is a LCST polymer. Examples of LCST polymers may be selected form the list comprising, and not limited to: poly((2-dimethylamino)ethyl methacrylate)) (PDMAEMA), poly(ethylene glycol methacrylate) (PEGMA), poly(N-vinyl caprolactam) (PNVCL), poly(ethylene oxide) (PEG), polypropylene oxide) (PPO), Poly(2- alkyl-2-oxazoline) (PEOx), poly (N-isopropylacrylamide) (pNiPAAm), poly(vinyl methyl ether) (PVME). More specific examples of the temperature-responsive LCST polymer encompass: poly(N- alkyl(meth)acrylamide) such as poly(N-isopropyl(meth)acrylamide), poly(N-n- propyl(meth)acrylamide), poly(N-methyl(meth)acrylamide), poly(N- ethyl(meth)acrylamide), poly(N-n-butyl(meth)acrylamide), poly(N- isobutyl(meth)acrylamide), and poly(N-t-butyl(meth)acrylamide); poly(N- vinylalkylamide) such as poly(N-vinylisopropylamide), poly(N-vinyl n- propylamide), poly(N-vinyl n-butylamide), poly(N-vinylisobutylamide), and poly(N-vinyl-t-butylamide); poly(N-vinylpyrrolidone); poly(2-alkyl-2-oxazoline) such as poly(2-ethyl-2-oxazoline), poly(2-isopropyl-2-oxazoline), and poly(2-n- propyl-2-oxazoline); polyvinyl alkyl ethers such as polyvinyl methyl ether and polyvinyl ethyl ether; a copolymer of polyethylene oxide and polypropylene oxide; poly(oxyethylene vinyl ether); cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose; and copolymers of the above polymers.

[0047] The hydrophilic polymer is a polymer providing a weight change (%), upon contact with water vapor at 90% relative humidity (RH) of at least 20%, preferably at least 30%, preferably at least 40%. In other words, according to the present embodiment of the invention, the hydrophilic polymer is a polymer provided to sorb water (swell) at 90% relative humidity (RH) thereby providing a polymer weight increase of at least 20% compared to the initial weight of the polymer, preferably at least 30%, preferably at least 40%. Hydrophilic polymers provided to sorb water to such extent that a polymer weight increase of at least 40% can be achieved, include, Poly(acrylic acid) salts, Polyethylene glycol, Poly(N-vinyl imidazole), Poly(2-methyl-2-oxazoline) poly(vinyl alcohol) (PVA). Hydrophilic polymers provided to sorb water to such extent that a polymer weight increase of at least 30% can be achieved, include, Poly(2- ethyl-2-oxazoline), Polyhydroxyethylmethacrylate and Poly(acrylic acid), whereas hydrophilic polymers provided to sorb water to such extent that a polymer weight increase of at least 20% can be achieved, include Poly[2 (Dimethylamino)ethyl Methacrylate], A list of weight changes for some of the polymers above can be found in H. M. L. Thijs, C. R. Becer, C. Guerrero-Sanchez, D. Fournier, R. Hoogenboom, and U. S. Schubert, “Water uptake of hydrophilic polymers determined by a thermal gravimetric analyzer with a controlled humidity chamber,” J. Mater. Chem., vol. 17, no. 46, pp. 4864-4871 , 2007.

[0048] The polymer is a crosslinked polymer. It has been found that crosslinked hydrophilic polymer nanofibers, provide for a faster water uptake and improved release behavior after a couple of sorption-desorption cycles compared to not crosslinked hydrophilic nanofibers. Hence, in a particular embodiment of the present invention, the hydrophilic polymer nanofibers comprise a polymer in a cross-linked state. The cross-linked state can be obtained by means of a variety of techniques part of the state of the art, such as by physical cross-linking, chemical cross-linking and enzymatic cross-linking. Physical cross-linking methods include UV-irradiation, energy electron beam, gamma irradiation, plasma treatment and dehydrothermal treatment, whereas chemical crosslinking methods include EDC, formaldehyde, glutaraldehyde, acrylamide, and others. Enzymatic methods include microbial transglutaminase methods. For example, the nanofibers can be crosslinked by means of UV-irradiation e.g. during solution electrospinning. In case the hydrophilic polymer according to the present invention is provided in a crosslinked state, said polymer is provided with crosslinkable functional groups adapted to provide said crosslinked state, such as and not limited to: cinnamate groups, benzophenone groups, amine groups, allyl groups, thiol-groups, selenol-groups, (activated) ester groups.

[0049] According to a further embodiment of the present invention, the polymer has a number average molar mass from about 5 000 to about 1 000 000 g / mol, preferably from about 10 000 to about 500 000 g / mol, more preferably from about 20 000 to about 300 000 g / mol. An advantage of the present embodiment is that a certain molar mass is required to provide chain entanglements and sufficient solution viscosity for electrospinning of nanofibers.

[0050] In the context of the present invention, by means of the term “nanofiber”, reference is made to a fiber having an average diameter from 100 nm up to about 3000 nm as measured by scanning electron microscopy. Nanofibers according to the present invention can be obtained according to various techniques in the state of the art, such as solution electrospinning, templatebased synthesis, sonochemical synthesis, self-assembly, polymerization, electro hydrodynamic writing, plasma induced synthesis, solution blow spinning, centrifugal jet spinning and CO2 laser supersonic drawing synthesis.

[0051] According to an embodiment of the present invention, the nanofibers are solution electrospun nanofibers, and have been hence solution electrospun. It has been found that solution electrospinning is particularly advantageous in providing the polymer nanofibers of the present invention.

[0052] In the context of the present invention, by means of the term “solution electrospun nanofiber”, reference is made to a nanofiber obtained by means of “solution electrospinning”. In the context of the present invention, by means of the term “solution electrospinning”, or “solution electrostatic spinning, reference is made to a process of producing fibers by applying a high voltage to a polymer solution to produce a polymer jet. In particular, solution electrospinning is a technique for creation of nano- or micro- scaled fibers from polymer solutions using an electric field. The pre-polymer is dissolved in a suitable solvent, placed in a capillary nozzle, and subjected to high electric field. As the liquid droplet of pre-polymer solution gets charged, the electrostatic repulsion overcomes the surface tension of the liquid, which leads to the formation of Taylor cone and ejection of the charged jet of pre-polymer solution from the capillary nozzle. The jet undergoes elongation and drying during the flight between capillary nozzle and is finally deposited on the grounded collector as nano- or micro- fibers.

[0053] The nanofibers suitably have an average fiber diameter from about 100 nm to about 3000 nm, preferably the nanofibers have an average fiber diameter from 200 nm to 1000 nm, more preferably the average diameter of the nanofibers is from about 400 nm to about 800 nm as measured by scanning electron microscopy.. It was found that when using nanofibers with these average diameters the adsorption rate is high, especially for air having a relative humidity of below 60%, preferably between 0%RH-30%RH or between 30%RH- 60%RH.

[0054] Where applicable, the polymer nanofibers may include appropriate quantities of any organic or inorganic additives that are customary in the field of plastics, such as fillers, reinforcing agents, plasticizers, stabilizers, dyes, slipping agents, wetting agents, dispersants, anti-clumping agents, anti-static agents, processing agents, blowing agents, and pigments.

[0055] The process may be applied for the sorption of water vapor. The process of the present invention is particularly advantageous in households to decrease ambient humidity and hence prevent mold formation, but they may be also used in application of dehumidifying and drying various gases, not limited to dehumidifying and drying of water vapor in the air. Applicable examples include methane gas, ethane gas, propane gas, butane gas, ethylene gas, acetylene gas, other hydrocarbon gases, hydrogen, carbon dioxide, carbon monoxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitrogen oxides, and ammonia gas, but the scope is not limited to these examples alone. The desiccant comprising nanofibers is preferably present as a layer of non-woven nanofibers of the cross-linked hydrophilic polymer. The desiccant, suitably as the layer of non-woven nanofibers, is suitably loaded onto a structure for increasing the contacting area of the gas and the desiccant. This loading may be on a surface, like a metal surface. The gas will then contact the desiccant by flowing the gas along the side of the layer which does not face the surface. The process may also be used as part of well known water collection or water retention processes.

[0056] Preferably the process is performed for removing water from air. The relative humidity of the air may be between 5 and 100%. High rates of removal have been observed when the relative humidity of the air is between 30 and 70%, preferably between 30 to 60%. The process is also suited to remove water from air having lower relative humidity ranges. Prior art processes are typically not very efficient in removing water from such low RH air streams while the present process is surprisingly more efficient for air streams having a relative humidity of below 40%, preferably below 30%, more preferably below 20% and even below 10%.

[0057] The temperature at which the gas contacts the desiccant may be any temperature at which the water adheres to the desiccant. This temperature may differ for different gasses. A preferred range for air is between 15 and 30 °C.

[0058] The desiccant will in the process gain weight due to the water as sorbed to the desiccant. The capacity of the desiccant to remove water will decrease in time. This used desiccant obtained in the process is preferably regenerated at a higher temperature than the temperature at which the gas contacts the desiccant. This regeneration may be performed by contacting a gas, which may be for example the feed gas, the dried gas or another gas, with the used desiccant to obtain a regenerated desiccant. The regenerated desiccant is then suitably reused in the process of this invention. The temperature at which the desiccant is regenerated is suitably between 10 and 60 °C higher than the temperature at which the gas contacts the desiccant and preferably between 10 and 40 °C higher than the temperature at which the gas contacts the desiccant. This difference in temperature is optimized to be as low as possible while still achieving sufficient regeneration. A low regeneration temperatures allows the use of lower temperature heat sources, such as generated by heat pumps and solar thermal collectors.

[0059] EXPERIMENTAL PART

[0060] In accordance with the present invention, several (PAOx based) polymers have been solution electrospun and measured for their moisture uptake properties.

[0061] MATERIALS AND METHODS

[0062] MATERIALS

[0063] Aquazol® 50 and 200 (poly-2-ethyl-2-oxazoline), also referred to respectively as AQ50 and AQ200, with a targeted molecular weight of respectively 50 000 and 200 000 g / mol are available from Sigma Aldrich (Overijse, Belgium). Benzophenone modified poly(2-ethyl-2-oxazoline) (PEtOx- PEI-BP) was synthesized according to literature (see Vergaelen et al., 2019). Cinnamate modified poly(2-ethyl-2-oxazoline) (PEtOx-PEI-CC) was synthesized based on literature (see Vergaelen et al., 2019). Polyvinylpyrrolidone (PVP) of the Kollodon® grade 90, also referred to as PVP K90, is available from BASF. Solvents used such as ethanol (>99.8%) and water (HiPerSolv CHROMANORM® used for DVS measurements) are available from VWR international (Leuven, Belgium) and used as such. Distilled water of type III as considered in ISO Standard 3696 was used when water was required for preparing solvent electrospinning or film casting solutions.

[0064] METHODS

[0065] Solvent electrospinning

[0066] Electrospinning solutions were prepared by dissolving varying amounts of polymer in the water-ethanol system. Mass concentrations are expressed by weight percentages (wt%) defined for the polymer as the ratio of polymer mass and the sum of the polymer and solvent mass (Eq. (1 )). All solution electrospinning experiments were carried out using a mononozzle, KD Scientific Syringe Pump Series 100, set-up with an 18-gauge Terumo mixing needle without bevel. A stable Taylor cone was achieved according to a tip-to-collector distance and a voltage (Glassman High Voltage Series EH-B) depending on the system. After electrospinning, all samples were stored in a climatized lab at 23°C ± 1 °C and a relative humidity of 25% ± 2%.

[0067] Scanning Electron microscopy

[0068] All produced membranes were analyzed on a Phenom XL Scanning Electron Microscope (SEM) at an accelerating voltage of 10 kV. Prior to analysis, the samples were coated with gold using a sputter coater (LOT MSC1T). The membranes were investigated for irregularities such as beads. The nanofiber diameters were evaluated via the FiberMetric software. The average diameters and their standard deviations are based on 500 measurements per sample.

[0069] Film casting

[0070] Polymer solutions were prepared as described for the solvent electrospinning solutions. The solutions were poured in an aluminum cup and left to evaporate all solvent under a fume hood for 48 hours. Afterwards the cups containing the polymeric films were stored in a climatized lab at 23°C ± 1 °C and a relative humidity of 25% ± 2%.

[0071] Crosslinking

[0072] All cross-linked membranes were cross-linked using an Osram Ultra Vitalux 300 watt Ultraviolet lamp. Samples were illuminated at a distance of 15 cm between the UV-lamp and the membrane. After crosslinking, all membranes were analyzed through SEM to ensure that the nanofiber morphology was unaltered by the UV irradiation.

[0073] Dynamic Vapor Sorption

[0074] Using a TA instruments Q5000 SA DVS device the moisture uptake of all membranes was measured. The used methods are described below.

[0075] For the AQ200 samples

[0076] First, an equilibrated drying step at 60°C and 0% RH, followed by an equilibration at 30°C and 0% RH is performed. Consequently, a stepwise humidity change of 10% RH was implemented from 0% to 90% and reverse. Each equilibrium step was aborted if the condition of less than 0.05% weight change for a period of 60 minutes was met, with a maximal step duration of 300 minutes.

[0077] - For the AQ50 samples

[0078] First, an equilibrated drying step at 40°C and 0% RH, followed by an equilibration at 30°C and 0% RH is performed. Consequently, a stepwise humidity change of 30% RH was implemented from 0% to 90% and reverse. This stepwise RH change was repeated. Each equilibrium step was aborted if the condition of less than 0.01 % weight change for a period of 12 minutes was met, with a maximal step duration of 300 minutes.

[0079] - For the PVP K90 samples

[0080] First, an equilibrated drying step at 40°C and 0% RH, followed by an equilibration at 30°C and 0% RH is performed. Consequently, a stepwise humidity change of 30% RH was implemented from 0% to 90% and reverse. This stepwise RH change was repeated. Each equilibrium step was aborted if the condition of less than 0.01 % weight change for a period of 12 minutes was met, with a maximal step duration of 300 minutes.

[0081] - For the PEtOx-PEI-BP and PEtOx-PEI-CC cross-linked membranes

[0082] First, an equilibrated drying step at 40°C and 0% RH, followed by an equilibration at 30°C and 0% RH is performed. Consequently, a stepwise humidity change of 30% RH was implemented from 0% to 90% and reverse. This stepwise RH change was repeated twice. Each equilibrium step was aborted if the condition of less than 0.01 % weight change for a period of 12 minutes was met, with a maximal step duration of 300 minutes.

[0083] Results were analyzed using the Universal analysis software provided via TA Instruments. Adsorption rates were calculated from the obtained data according to the rate at which 80% of the weight gain was obtained (Eq. (2)). Through this method, the stagnant equilibrium period is excluded from the calculations as the final weight gain percentages can significantly influence the result due to the equilibrium procedure.

[0084] Example 1 : Moisture sorption of Aquazol® 200 powder vs. nanofibers

[0085] An AQ200 nanofibrous membrane was solvent electrospun and its moisture sorption was compared to the unprocessed AQ200 powder. As seen in Fig. 1 the nanofibrous membrane is able to sorb more moisture compared to the powderous AQ200 (43 wt% vs. 41 wt%), moreover the sorption and desorption process is significantly faster for the nanofibrous samples in comparison to its powderous counterpart. The enhanced adsorption rate is clearly demonstrated in Fig. 2. It can be concluded that the nanofibrous morphology has a significant accelerating effect on the rate at which moisture is sorbed.

[0086] In particular, Fig. 1 illustrates the moisture sorption kinetics of both AQ200 nanofibers and AQ200 powder. The provided time vs. weight change plot illustrates the reduced time needed for the nanofibrous AQ200 to reach equilibrium in between steps. This is a result of a faster moisture uptake (see Fig. 2) and ultimately results in an accelerated completion of the imposed test method compared to powderous AQ200.

[0087] Fig. 2 illustrates the adsorption rate for each adsorption step of both AQ200 nanofibers (black) and AQ200 powder (white). The provided plot illustrates the increased adsorption rate of the nanofibrous sample due to its increased surface area in comparison to AQ200 powder. Example 2: Moisture sorption of Aquazol® 50 powder vs. films vs. nanofibers

[0088] Several AQ50 samples were prepared to be measured for their moisture sorption. Three nanofibrous membranes were solvent electrospun out of three solvent electrospinning solutions consisting of three different AQ50 concentrations. As a result, three membranes with different nanofiber diameters of 210, 575 and 2967 nm were obtained. A solvent casted AQ50 film was prepared according to the described method. The moisture sorption of these four samples was compared to each other and to that of the unprocessed AQ50 powder. As seen in Fig. 3 the nanofibrous membranes are able to go through the imposed sorption and desorption process significantly faster compared to both the AQ50 film and powder in the first sorption-desoprtion cycle. This advantage is significant for the first imposed adsorption run, while in the second adsorption run the advantage of the nanofibers is lost due to their lack of moisture stability (not shown). At 90% RH the hydrophilic AQ50 nanofibers have lost their fiber morphology and transformed into films due to the water uptake, which is irreversible. As the AQ50 film has no morphology to lose, this effect is not noticed, and its sorption remains consistent for the two imposed adsorption / desorption cycles. However, due to the significantly lower surface area of the AQ50 film and powder, the adsorption rate of the nanofibrous membranes is significantly faster, as shown in Fig. 4. Remarkably, the nanofibrous membrane with the smallest fiber diameter, and hence largest surface area, does not display the highest adsorption rate, in accordance with the present invention that the sorption rate is not linearly dependent on the nanofiber surface area. The highest adsorption rate is seen for the membrane with an average fiber diameter of around 575 nm, suggesting that there is an optimum for moisture sorption.

[0089] Fig. 3 illustrates the moisture sorption kinetics (first sorption-desorption cycle) of AQ50 film, AQ50 powder (referenced on the plot with arrows) and three AQ50 nanofibrous membranes with a varying fiber diameter; 210 ± 85 nm (solid line), 575 ± 103 nm (dashed line) and 2967 ± 275 nm (dash - dot line). The provided time vs. weight change plot illustrates the reduced time needed for the nanofibrous AQ50 to reach equilibrium in between steps for the first imposed adsorption cycle. This is a result of a faster moisture uptake (see Fig. 4) compared to powderous and film casted AQ50.

[0090] Fig. 4 illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of (form left to right for each RH change range respectively) AQ50 powder, AQ50 film, and three AQ50 nanofibrous membranes with a varying fiber diameter; 210 ± 85 nm, 575 ± 103 nm and 2967 ± 275 nm. The provided plot illustrates the significantly increased adsorption rate of the nanofibrous samples for the 0% - 30% RH and 30% - 60% RH steps, due to its increased surface area in comparison to AQ50 powder. For the 60% - 90% RH step the advantage of increased surface area is lost due to loss of fiber morphology. Remarkably, the nanofibrous membrane with the smallest fiber diameter, and hence largest surface area, does not display the highest adsorption rate. This highest adsorption rate is seen for the membrane with an average fiber diameter of around 575 nm.

[0091] Example 3: Moisture sorption of cinnamate modified polv(2-ethvl-2-oxazoline) nanofibers

[0092] Two PEtOx-PEI-CC nanofibrous membranes were solvent electrospun and cross-linked under UV-irradiation for 120 minutes. Subsequently, both membranes with a different nanofiber diameter were analyzed for their moisture sorption properties. As seen in Fig. 5, both membranes behave much alike. Moreover, it is clear that the second and third cycle are almost identical, indicating that the sample does not alter in between the cycles. There is a slight difference between cycle one and two, which can be attributed to a certain swelling of the nanofibers. However, as plateau equilibriums are still reached, it is safe to say that the crosslinking was effective in keeping the PEtOx based nanofibers moisture stable. Comparing the weight change of the non-cross- linked membranes (43%) to that of the PEtOx-PEI-CC cross-linked membranes (36%) a small decrease is observed. However, as shown in Fig. 6, this hardly affects the adsorption rate. Moreover, again it is seen that after the initial cycle at which the membrane goes to an equilibrium morphology, cycle two and three behave identical, unlike the non-cross-l inked membranes which behave similarly to powderous PEtOx after cycle one. Once more, this corroborates the successful crosslinking of the membranes. Additionally, in accordance with the present invention, the membrane with the largest nanofiber diameter exhibits the largest adsorption rate out of both membranes.

[0093] Fig. 5 illustrates the moisture sorption kinetics of two PEtOx-PEI-CC cross-linked nanofibrous membranes with a varying fiber diameter; 456 ± 75 nm (black) and 659 ± 105 nm (light gray). The provided time vs. weight change plot illustrates the similar behavior between both cross-linked samples. Equilibriums plateaus are reached in each cycle, without much difference between cycles. Consequently, it is safe to say that the crosslinking was effective in keeping the PEtOx based nanofibers moisture stable without large alteration in membrane morphology.

[0094] Fig. 6 illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of two PEtOx-PEI-CC cross-linked nanofibrous membranes with a varying fiber diameter; 456 ± 75 nm (black) and 659 ± 105 nm (white). The provided plot illustrates the similarity between cycle two and three, indicating that, after the initial cycle at which the membrane goes to an equilibrium morphology, the crosslinking of the membranes was successful. Additionally, in accordance with the present invention, the membrane with the largest nanofiber diameter exhibits the largest adsorption rate out of both membranes. Moreover, the average adsorption rate is significantly higher compared to that of powderous PEtOx, i.e., AQ 50 or AQ200. Additionally, the adsorption rate remains constant after cycle one, unlike non-cross-linked nanofibrous PEtOx, which loses the advantage of a high surface area after one cycle.

[0095] Example 4: Moisture sorption of benzophenone functionalized polv(2-ethyl-2- oxazoline) nanofibers

[0096] Four PEtOx-PEI-BP nanofibrous membranes were solvent electrospun and cross-linked via UV light for a certain time. Consequently, all membranes, with varying nanofiber diameters, were analyzed for their moisture sorption properties. As seen in Fig. 7, all membranes behave alike. Moreover, as plateau equilibriums are reached during each cycle, it is indicated that the sample does not alter in between the cycles and hence, it is safe to say that the crosslinking was effective in keeping the PEtOx based nanofibers moisture stable. Comparing the weight change of the non-cross-linked membranes (43%) to that of the PEtOx-PEI-CC cross-linked membranes (28%) a decrease is observed. However, as shown in Fig. 8A and B, this does not affect the adsorption rate. Moreover, all cycles exhibit a similar adsorption rate, unlike the non-cross-linked membranes, which behave similarly to powderous PEtOx after cycle one. Once more, this corroborates the successful crosslinking of the membranes. Additionally, in accordance with the present invention, no direct relationship between nanofiber surface area (that increases with decreasing fiber diameter) and adsorption rate can be observed.

[0097] Fig. 7 illustrates the moisture sorption kinetics of four cross-linked PEtOx- PEI-BP nanofibrous membranes with a varying fiber diameter and duration of crosslinking; 475 ± 93 nm and 45 min UV, 321 ± 64 nm and 40 min UV, 787 ± 108 nm and 60 min UV and 783 ± 95 nm and 90 min UV. The provided time vs. weight change plot illustrates that all membranes behave alike and reach equilibrium plateaus cycle. Thus, indicating that the crosslinking was effective in keeping the PEtOx based nanofibers moisture stable without large alterations in membrane morphology.

[0098] Fig. 8A and Fig. 8B illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of four cross-linked PEtOx-PEI-BP nanofibrous membranes with a varying fiber diameter and duration of crosslinking (from left to right, for each RH change range respectively); 321 ± 64 nm and 40 min UV, 475 ± 93 nm and 45 min UV, 787 ± 108 nm and 60 min UV and 783 ± 95 nm and 90 min UV. In Fig. 8B, a, b and c represent a closer look at the results for each cycle. The provided plot illustrates a similar adsorption rate for the membranes throughout the different cycles, unlike the non-cross- linked membranes, which behave similarly to powderous PEtOx after the initial cycle by losing the advantage of a high surface area. Moreover, compared to powderous PEtOx, higher adsorption rates are achieved. Furthermore, in accordance with the present invention, no direct relationship between nanofiber diameter and adsorption rate can be observed.

[0099] Example 5: Moisture sorption of PVP K90 film vs. nanofibers

[0100] Several PVP K90 samples were prepared to be measured for their moisture sorption. Four nanofibrous membranes were solvent electrospun out of four solvent electrospinning solutions consisting of four different PVP K90 concentrations. As a result, four membranes with different nanofiber diameters of 280, 318, 482 and 947 nm were obtained. A solvent casted PVP K90 film was prepared according to the described method. The moisture sorption of these five samples was compared to each other. Fig. 9 illustrates the moisture sorption kinetics of PVP K90 film (black) and four PVP K90 nanofibrous membranes (grey) with a varying fiber diameter; 280 ± 48 nm (solid line), 318 ± 54 nm (dashed line), 482 ± 71 nm (long-dash-dash line) and 947 ± 145 nm (long-long line). The provided time vs. weight change plot illustrates the reduced time needed for the nanofibrous PVP K90 to reach equilibrium in between steps for the first imposed adsorption cycle. This is a result of a faster moisture uptake (see Fig. 10) compared to film casted PVP K90. As seen in Fig. 9 the nanofibrous membranes are able to go through the imposed sorption and desorption process significantly faster compared to the PVP K90 film. This advantage is significant for the first imposed adsorption run, while in the second adsorption run the advantage of the nanofibers is lost due to their lack of moisture stability. At 90% RH the hydrophilic PVP K90 nanofibers have lost their fiber morphology and transformed into films due to the water uptake, which is irreversible. As the PVP K90 film has no morphology to lose, this effect is not noticed, and its sorption remains consistent for the imposed adsorption / desorption cycles. However, due to the significantly lower surface area of the PVP K90 film, the adsorption rate of the nanofibrous membranes is significantly faster, as shown in Fig. 10. Fig. 10 illustrates the adsorption rate for each adsorption step of the first imposed adsorption cycle of (form left to right for each RH change range respectively) PVP K90 film, and four PVP K90 nanofibrous membranes with a varying fiber diameter; 280 ± 48 nm, 318 ± 54 nm, 482 ± 71 nm and 947 ± 145 nm. The provided plot illustrates the significantly increased adsorption rate of the nanofibrous samples for the 0% - 30% RH and 30% - 60% RH steps, due to its increased surface area in comparison to PVP K90 film. For the 60% - 90% RH step the advantage of increased surface area is lost due to loss of fiber morphology. Remarkably, the nanofibrous membrane with the smallest fiber diameter, and hence largest surface area, does not display the highest adsorption rate. This highest adsorption rate is seen for the membrane with an average fiber diameter of around 482 nm.

[0101] Remarkably, the nanofibrous membrane with the smallest fiber diameter, and hence largest surface area, does not display the highest adsorption rate, in accordance with the present invention that the sorption rate is not linearly dependent on the nanofiber surface area. The highest adsorption rate is seen for the membrane with an average fiber diameter of around 482 nm, suggesting that there is an optimum for moisture sorption.

Claims

CLAIMS1 . A process to remove water from a gas by contacting the gas with a desiccant comprising nanofibers of a cross-linked hydrophilic polymer.

2. The process according to claim 1 , wherein the nanofibers of the desiccant have an average diameter from about 100 nm to about 3000 nm.

3. The process according to claim 2 , wherein the nanofibers have an average diameter from 200 nm to 1000 nm.

4. The process according to claim 3, wherein the average diameter of the nanofibers is from about 400 nm to about 800 nm.

5. The process according to any one of the previous claims, wherein the polymer is a thermoresponsive polymer.

6. The process according to any one of claims 1 -5, wherein the cross-linked hydrophilic polymer is selected from the list comprising: Poly(2- alkyl-2- oxazoline) (PEOx), Poly(acrylic acid) (PAA), Polyethylene glycol (PEG), Polyhydroxyethylmethacrylate (PHEMA), Poly(N-vinyl imidazole) (PVIM), Poly[2 (Dimethylamino)ethyl Methacrylate] (PDMAEMA), Polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), pullulan, chitosan, keratine, gelatin, salts, derivatives and copolymers thereof.

7. The process according to claim 6, wherein the polymer is a Poly(2- alkyl- 2-oxazoline).

8. The process according to claim 7, wherein the Poly(2- alkyl-2-oxazoline) is selected from the list comprising: Poly(2- ethyl-2-oxazoline) (PEtOx), Poly(2-methyl-2-oxazoline) (PMeOx).

9. The process according to claim 8 wherein the Poly(2- alkyl-2-oxazoline) is Poly(2-ethyl-2-oxazoline).

10. The process according to any one of the previous claims, wherein the polymer has a number average molar mass from about 5 000 to about 1 000 000 g / mol.

11. The process according to claim 10, wherein the polymer has a number average molar mass from 20 000 g / mol to 300 000 g / mol.

12. The process according to any one of the previous claims, wherein the nanofibers are solution electrospun nanofibers.

13. The process according to any one of claims 1 -12, wherein the desiccant does not contain LiCI.

14. The process according to any one of claims 1 -13, wherein the desiccant is present as a layer of non-woven nanofibers of the cross-linked hydrophilic polymer.

15. The process according to claim 14, wherein the layer is supported by a surface and wherein the gas contacts the desiccant by flowing the gas along the side of the layer which does not face the surface.

16. The process according to any one of claims 1 -15, wherein the gas from which water is removed is gaseous methane, ethane, propane, butane, ethylene, acetylene, hydrogen, carbon dioxide, carbon monoxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitrogen oxides and / or ammonia.

17. The process according to any one of claims 1 -15, wherein the gas from which water is removed is air.

18. The process according to claim 17, wherein the air as contacting the desiccant has a relative humidity of between 30 and 70%.

19. The process according to any one of claims 1-18, wherein the temperature at which the gas contacts the desiccant has a temperature of between 15 and 30 °C.

20. The process according to any one of claims 1-19, wherein the desiccant obtained in the process is regenerated at a higher temperature than the temperature at which the gas contacts the desiccant to obtain a regenerated desiccant and wherein the regenerated desiccant is reused in the process.21 . The process according to claim 20, wherein the temperature at which the desiccant is regenerated is between 10 and 60 °C higher than the temperature at which the gas contacts the desiccant.

22. The process according to claim 21 , wherein the temperature at which the desiccant is regenerated is between 10 and 40 °C higher than the temperature at which the gas contacts the desiccant.

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