The invention relates to a membrane, a use and a method for manufacturing thereof, and a method for pressureless oxygen-enrichment of the air. The invention relates to a field of oxygen-transporting membranes.

A method for membrane oxygen-enrichment of the air by use of pyrolytic carbon membranes, which function on the basis of „molecular sieves” (i.e. larger stays, smaller passes) is known in the art. However, this method requires use of a high pressure difference at both sides of the membrane, which involves use of additional equipment and membranes of special structures. A number of layered membranes operating on the same principle, i.e. utilizing a high pressure difference and a small diffusion coefficient, were proposed, which result, however, in low enrichment effectiveness and very limited applications. A traditional, effective method for the oxygen-enrichment of the air is its liquefaction and rectification (distillation), which is yet very expensive.

To increase effectiveness of a process for oxygen-enrichment of the air, so-called magnetic membranes, comprising particles with magnetic properties dispersed in a matrix, were proposed. Working of such membranes is based on utilizing paramagnetism of oxygen and diamagnetism of nitrogen, as well as insensibility of remaining air components to a magnetic field. For instance, the publications JP59109205A, JP58112022A and JP63291621A disclose membranes used for selective transport of oxygen, comprising powdery particles with magnetic properties dispersed uniformly in a matrix. The obtained membranes were further exposed to an external magnetic field. Such membranes had better properties of oxygen selectivity compared to the traditional membranes, however they did not eliminate necessity of utilizing an air pressure difference. The attractive force of a magnetic field for oxygen was not strong enough to generate a chemical potential gradient of oxygen, and then causes its diffusion.

The publication JP2008018338A discloses a membrane used for oxygen-enrichment of the air, comprising particles with magnetic properties dispersed between the first and the second membrane surface generating a concentration gradient along the membrane thickness, and consequently a magnetic field gradient. The particle concentration gradient is uniform along the entire thickness of the membrane and can be continuous or stepwise (layered). A driving force of the process for oxygen-enrichment of the air employing this membrane is an air pressure difference at both sides of the membrane, which causes oxygen to diffuse in a direction of the lower pressure. The diffusion can be further enhanced by oxygen being attracted to the dispersed particles with magnetic properties, in a direction from the lower particle concentration to the higher particle concentration. In spite of the observed excellent transport properties of the membrane, the need of applying the pressure difference has not been eliminated. Therefore, in case of thin membranes, the inventors consider use of additional porous supports.

In publication by P. Borys, K. Pawelek, Z. J. Grzywna, On the magnetic channels in polymer membranes, Phys. Chem. Chem. Phys., 13, 17122-17129, 2011 there are raises doubts about attracting molecules of oxygen by a magnetic field gradient generated by particles with magnetic properties in a membrane.

An object of the present invention is providing a membrane and a method which enables oxygen-enrichment of the air, with no air pressure difference applied at both sides of the membrane.

The invention relates to an oxygen transporting membrane comprising a matrix and particles with magnetic properties dispersed therein, wherein a concentration of particles with magnetic properties increases between one internal membrane surface and the other internal membrane surface, generating a concentration gradient along the membrane thickness, and lines of a magnetic field generated by the particles with magnetic properties extend along the membrane thickness and their direction is consistent with the direction of said concentration gradient, characterized in that the concentration gradient of the particles with magnetic properties is a discrete gradient.

In a preferred embodiment of the invention, the particles with magnetic properties are, relative to the matrix, a separate phase, which adheres to one of the internal membrane surfaces. Preferably, the matrix is a polymer matrix.

In another embodiment of the invention, the amount of the particles with magnetic properties dispersed in the matrix is from more than 0 to 90 % by weight.

Preferred average grain size of the particles with magnetic properties is from 5 to 50 pm.

The invention relates also to a use of the above-defined membrane in window panes, windows, greenhouses, films, oxygen masks, oxygen tents and oxygen chambers.

The invention relates also to a method for pressureless oxygen-enrichment of the air, comprising contacting the external surface of the membrane as defined above, from a side with the higher concentration of particles with magnetic properties in the membrane, with the air, the air undergoing oxygen-enrichment in a direction of the lower concentration of the particles with magnetic properties in the membrane. Moreover, the invention relates to a method for manufacturing of a biphasic, heterogenous magnetic membrane, comprising the following steps of: a) dissolving a polymer in a solvent; b) dispersing particles with magnetic properties in the mixture obtained in the step a); c) casting the dispersion obtained in the step b) on a surface of a shape corresponding to a surface of the obtained membrane; d) sedimentation of particles with magnetic properties to form a polymer phase and a magnetic phase; e) evaporating the solvent; f) exposing the obtained membrane to an external magnetic field, the lines of the external magnetic field extending along the membrane thickness and being directed towards the magnetic phase.

Preferably, the evaporation of the solvent of the step e) may be conducted during the sedimentation of the step d).

The step f) can be also conducted simultaneously with the steps e) and d).

Moreover, the step f) may be conducted during the step d) or during the step e).

In preferred embodiments of the method, the amount of the polymer in the mixture obtained in the step a) is from 3 to 5 % by weight, the amount of the particles with magnetic properties in the dispersion obtained in the step b) is from 1 to 11 % by weight, and the external magnetic field induction value in the step f) is from more than 0 to 40 mT.

The polymer is preferably a low density polymer.

In the membrane of the present invention, almost all particles of the material with magnetic properties adhere to one of the internal membrane surfaces. As a result, the particles of the material with magnetic properties generate a discrete magnetic field gradient between one internal membrane surface and the other internal membrane surface, consistent with the particle concentration gradient. In the method of pressureless oxygen-enrichment of the air of the invention, the magnetic field at the side of the membrane with a higher concentration of the particles with magnetic properties attracts molecules of oxygen, generating the chemical potential gradient of oxygen, and then inducing diffusion of oxygen through the membrane from the side with a higher concentration of the particles with magnetic properties, in the direction of the side with a lower concentration of the particles with magnetic properties. In this way, the air is enriched with oxygen at the side of the membrane with a lower concentration of the particles with magnetic properties and, at the same time, is depleted in oxygen at the side with a higher concentration of the particles with magnetic properties. A driving force of this process is the discrete magnetic field gradient. In contrast to membranes of the prior art, no pressure difference is required, and consequently there is no need to employ additional equipment, and the membranes are not subject to damage by a high pressure, regardless of their thickness and structure. The invention has been shown in the following exemplary embodiment.

The magnetic membranes with matrices from EC (ethylcellulose), HBPI (a highly branched polyimide) and LPI (a linear polyimide) were prepared by casting from a solution. In a solvent, a suitable amount of the polymer, i.e. 5 % by weight for EC, 4 % by weight for LPI and 3 % by weight for HPBI, based on a solvent, was dissolved. In case of EC, the solvent was a mixture of ethanol and toluene in the 40:60 ratio, and in case of HBPI and LPI, the solvent was N-methylpyrrolidone. Then a material with magnetic properties (i.e. magnetic powder) in a suitable amount (indicated in Table) was dispersed, the obtained dispersion was homogenized, and then cast into a Petri dish and the solvent was allowed to slowly (48 hours) evaporate under a filter paper cover. In the course of the solvent evaporation process, the magnetic powder sedimented to obtain the biphasic membrane (with the magnetic and polymer layers). After 2 days the membrane was collected from the Petri dish, washed and dried at 40 °C. The last step of the preparation of the magnetic membranes was their magnetization in a pulse field magnet with induction of about 2.5 T. The lines of magnetic field and their direction were consistent with a magnetic powder concentration gradient. The results for the membranes with the three different matrices and for three different thicknesses and the same amount of three different powders are reported in the following table:

Table

* - values for the respective granulations of a given powder

- a value of 3% in the table corresponds to an increase of the oxygen level of 3% to the final level of 24% etc. ** - MQFP-B - an alloy of the composition: Nd-Fe-Co-B, MQP-14-12 - an alloy of the composition: Nd-Pr-Fe-B, NdFeB - an alloy of the composition: Nd-Fe-B; manufactured by Magnequench Company, % content of elements not disclosed by the manufacturer

In case of prototyping of a window, studies were conducted for a membrane, a polymer matrix of which comprised cellulose acetate in the amount of 18,7 % by weight, and a filling comprised neodymium in the amount of 81,3 % by weight, with the grain size of 20 pm. The studies were conducted in measuring vessels of capacities of 50 ml and 100 ml, where the hole diameters for the membrane were 4 cm and 6 cm, respectively. Vessel rims were lubricated with a silicone grease and sealed with the membrane, suitably trimmed to vessel dimensions. The entire assembly was pressed down with a ring and tightened with screws. At the bottom of the vessel an oxygen sensor with an oxygen meter was provided, which was previously calibrated on the air in the room. The studies were conducted for 36 hours, with the oxygen content checked each hour. The amount of oxygen was found to increase or decrease depending on the side of the membrane exposed outside the measuring vessel. At first, the amount of oxygen was changing rapidly, but as the time elapsed, the oxygen concentration in the vessel was changing very slowly. After 36 hours, an increase of oxygen concentration of about 8% was observed.

Based on the data above, it can be stated that the membrane of the invention allows to enrich the air in oxygen with no air pressure difference applied at both sides of the membrane. The invention can be applied in any place where oxygen-enrichment of the air is needed, e.g. in window panes, greenhouses, films, oxygen masks, oxygen tents and oxygen chambers. Since, in parallel to the process of oxygen-enrichment of the air, an oxygen- depletion of the air proceeds on the other side of the membrane, the invention can also be applied in any place where low level of oxygen is required, e.g. wrappings for food and drugs.