LIQUID INTERFACES OF HYGROSCOPIC CELLULOSIC STRUCTURES

Background of the Invention

Field of the Invention

[0001] The present invention concerns a process for the water-induced sorption of small particulate matter from a process feed consisting of air into a hygroscopic assembly.

[0002] Particularly, the hygroscopic assembly is prepared from a cellulosic biomaterial.

Description of Related Art

[0003] Forest derived materials are gaining an increasingly important role as functional materials due to their ability to positively address global challenges such as resource sufficiency, climate change and urbanization. [0004] These forest derived materials can be utilized, e.g. by exploiting the inherent hydrophilicity and hygroscopicity of wood-derived cellulosic building blocks, which are highly advantageous features supporting the requirements of many such functional materials and applications. [0005] Using such forest derived materials as e.g. membranes and filters, it is possible to relieve global environmental problems, such as scarcity of clean air and water, as well as agricultural resource sufficiency and urbanization.

[0006] Pollutants in air and water include many types of small particles, some of which are even inhalable and cause health adversities. Such inhalable particle pollution typically contain particles having diameters of less than lOpm, including among others dust and pollen, as well as fine particles even smaller than 2.5pm, including among others combustion particles, organic compounds and metals.

[0007] KR101551850B describes the formation of a porous filter structure for dust removal, by performing solvent exchange, on microfibrillated cellulose, from water to non-polar solvent, followed by freeze-drying. Similarly, US2012039756A1 and WO2015187412A1, as well as several other publications, describe the use of microfibrillated cellulose in manufacturing filters for use in purifying e.g. air or other gases. However, the described structures are not suitable for capturing pollutants through water interactions.

[0008] Further, CN105498550 describes the preparation of a non-woven fabric composite nanofiltration membrane and its application in water treatment. However, said membrane is used as a typical water filter, instead of using it at a gaseous water-air interface.

[0009] Thus, there is still a significant need for improved and environmental technologies to capture air pollutants.

Summary of the Invention

[0010] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0011] According to a first aspect of the present invention, there is provided a process for the water-induced sorption of small particulate matter from a gaseous process feed into a hygroscopic assembly.

[0012] According to a second aspect of the present invention, there is provided a process, wherein the small particulate matter includes particles carried by air or water, especially particles incorporated with water in air (i.e. with the moisture in air). [0013] According to a third aspect, there is provided a process, wherein the utilized assembly is made of a hygroscopic cellulosic biomaterial. The hygroscopic assembly provides a route to capture particles, which have been incorporated with water in air, through adsorption at solid-gas interface.

[0014] Therefore, we propose a new biobased concept to capture, concentrate, and store moisture and particles from air and water, especially from air and from air- water interfaces. [0015] According to a preferred alternative, the concept is based on foams and porous structures that capture moisture and particles, where the capture takes place via a water-induced procedure, i.e. typically by utilizing the hygroscopic properties of the biomaterial. [0016] Several advantages are achieved using the present invention. The fibrillar network of the assemblies will provide high surface area, strength, stability and controllable density/porosity balance for optimal capturing capacity and gas/liquid permeability. Brief Description of the Drawings

[0017] FIGURE 1: Scanning electron microscopy image of hygroscopic cellulose based structure (a) with particulate matter absorbed into the structure (b) and a schematic illustration of the sorption process (c). Embodiments of the Invention

[0018] Definitions

In the present context, the term "nanoscale cellulose" is intended to encompass cellulose nanofibers (CNF), microfibrillated cellulose (MFC), nanocrystalline cellulose (NCC) or bacterial nanocellulose. The size of the fibers in these materials is typically 2-500 nm in width, preferably 2-50 nm.

The "small particulate matter", in turn, is intended to encompass molecules and other small dust-forming particles, typically having a particle size of <10pm, preferably <100 nm.

The term "RH", means the relative humidity, and is surprisingly not an essential feature of the invention. In fact, the invention, and causing the induction of the sorption of the particulate matter of the process feed into the assembly of the invention, functions at all levels of humidity. Preferably the RH level is, however, 50% or more, most suitably at least 75%. The term "porous" is intended to cover all materials having a pore size of 2- lOOOnm, particularly 2-100nm.

[0019] The present invention relates to a process for water-induced sorption of small particulate matter from a process feed selected from air or water, particularly by providing an assembly prepared from a hygroscopic biomaterial based on nanoscale cellulose, allowing it to absorb vaporous or liquid water to a level of at least 50 %RH, to cause a water-induced structural reconfiguration, and finally placing the assembly in contact with air or water containing particulate matter, while maintaining said %RH level in the structure throughout the contacting. [0020] The biomaterial utilized in the invention is typically a cellulosic biomaterial that is capable of forming a 2D or 3D porous network. An example of such a material is cellulose nanofibrils.

[0021] According to an embodiment of the present invention, the biomaterial is obtained from any fibrous plant-based source which can be processed to fibrous structures, preferably from a wood-based source, more preferably from a pulped wood- based source.

[0022] The assembly prepared from a hygroscopic biomaterial is preferably a porous 2D or 3D assembly. The pore size of such an assembly is typically 2-100nm, while a preferred porosity is >95%, most suitably >99%. Such a porosity allows the controlled passage for assisting gaseous components with sufficient contact points for capturing molecules, or the particulate matter mentioned above.

[0023] Said high porosity is typically linked with a low density, which for the biomaterial of the present invention preferably is at a level of l-50g/l.

[0024] According to an embodiment of the invention, the assembly is shaped into one or more layers to form the desired structure for the assembly.

[0025] An example of hygroscopic materials is cellulose nanofibrils. Upon isolation of these cellulose nanofibrils (CNFs) from their native surroundings, their inherently high hydroxyl group density and the consequential hydrophilic and hygroscopic nature is preserved.

[0026] These structural features have an effect on water interactions and transport mechanisms (capillary actions, diffusion, swelling) taking place within the material.

Exploiting and manipulating the binding and transport of molecules, such as said small particulate matter, will enable the construction of materials for moisture and nutrient capturing. [0027] These transport mechanisms thus include capillary actions, diffusion and swelling, and are in the present invention utilized to capture moisture, and via the moisture also particulate matter from the process feed. These mechanisms are different from ion exchange, among others, by not binding and releasing chemicals by extracting and eluting.

[0028] The hygroscopic nature of these materials facilitates the capturing of also large volumes of water.

[0029] Water acts as a carrier for the emissions, such as the small particulate matter. Therefore, this procedure relies on both hydrophilicity and hygroscopicity.

[0030] The capturing typically results in a pressure drop, since the number of particles at the inlet of the assembly is larger than the number of particles at the outlet of the assembly. The pressure drop is, however, preferably at a low level, such as a level of lOOPa or less, more preferably 50Pa or less.

[0031] The assemblies of the invention can be prepared using any existing technologies for film manufacturing, 3D-printing and foam forming, e.g. 2D structuring via film casting, web forming, or 3D structuring via 3D-printing, foam forming or web forming.

[0032] Using such techniques, it is possible to produce virtually any nanocellulose grade.

[0033] The assemblies used in the invention are typically nanoporous structures with high moisture capturing ability.

[0034] Preferably, these structures are shaped as macroscaled 3D structures with tunable porosity, prepared by using highly hydrophilic nanocellulosic building. Preferably these structures are shaped as films or 2D or 3D macro-scaled structures. [0035] The hygroscopicity of the used cellulosic materials coupled with the above- mentioned porosity will provide a high capturing capacity.

[0036] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0037] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an

embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0038] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0039] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details. [0040] While the forgoing examples are illustrative of the principles of the present invention, it is not intended that the invention be limited, except as by the claims set forth below.

[0041] The following non-limiting examples are intended merely to illustrate the advantages obtained with the embodiments of the present invention.

EXAMPLES

Example 1 - Assessing the performance of constructed assembly structures

[0042] Particle filtration tests were used to assess performance of constructed structures in capturing Ti0 ₂ (diameter = 100-600 nm). The tests were carried out as function of water vapour content to reveal the potentially enhancing effect of humidity in compound capturing.

[0043] The results obtained from these tests were as follows:

- Decontamination factor (DF) (= number of particles at inlet / number of particles at outlet) 2000 with 40 Pa pressure drop.

Industrial Applicability

[0044] The present process can be used to prepare filters and other similar 2D and 3D structures that can be used for capturing and optionally valorizing pollutants from air. Citation List

Patent Literature

CN105498550 KR101551850B

US2012039756A1

WO2015187412A1