Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-02-23
2001-09-25
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S490000, C426S504000, C426S402000, C426S425000
Reexamination Certificate
active
06294092
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to a new container useful for the preparation of rehydrated solute solutions, of rehydrated blood products, of nutritional solutions, of solutions for medical purpose or of pure water, comprising a semi-permeable membrane material with a low molecular weight cut-off, to its use in a process of osmotically driven filtration and for the manufacture thereof.
BACKGROUND OF THE INVENTION
In view of its intended uses, the wall of a container (or a portion thereof) useful for the preparation of rehydrated solute solutions, of rehydrated blood products, of nutritional solutions, of solutions for medical purposes or of pure water by osmotically driven filtration, consists generally in a semi-permeable membrane.
Thus, a semi-permeable membrane needs to be strong, relatively inert and capable of separating compounds with different molecular weights. A semi-permeable membrane structure is characterized by its molecular weight cut-off (MWCO) defined by the molecular weight at which 90% of the solute will be prevented from permeating through the membrane. Since the permeability of a membrane with a given molecular weight cut-off is proportional to its thickness, the lower the molecular weight cut-off, the lower the thickness of the membrane must be to maintain practical flux rates. However, the thinner this membrane becomes, the lower its strength. On the other hand, the higher the molecular weight cut-off, the more the phenomenon of dialysis can interfere with osmosis. Moreover, the lower the molecular weight cut-off, the more selective the semi-permeable membrane. There are thus advantages of working with a molecular weight cut-off as low as possible while maximizing flux rate.
STATE OF THE ART
The European Patent EP 360612 discloses a process wherein an accurately controlled mixture of low molecular sugar and electrolyte salts, which together form the basis of an oral rehydration treatment, is retained into a leak proof container constructed from a semi-permeable membrane which may be of cellulose, regenerated cellulose, benzoylated cellulose, viscose cellulose and collagen. This membrane has a molecular weight cut-off below the molecular size of microorganisms or enterotoxins of
V. Cholerae
and Shigella species so that when the container and contents are placed into water containing the said contaminants, a process of osmosis takes place where water free from contaminants is drawn into the container, but where the passage of micro-organism into the container is prevented, resulting in a sterile oral rehydration solution inside the container. In this disclosure, the concentration of the sterile content of the container is controlled by achieving an equilibrium between the osmosis and dialysis of the sugars and electrolytes into the external water. Therefore, the final concentration of solution is dictated by the quantity of solute within the container and the volume of external water. The disadvantages of this system are an expensive loss of solute, the growth of bacteria in the external water due to sugars (nutrient) feeding, the need to precisely control the volume of external water and the low efficiency of the device, i.e. amount of water taken up in a given period being low due to dialysis of solute.
Aims of the Invention
The present invention aims to provide a container which does not present these drawbacks. The aim of the invention is to provide a container comprising a flexible membrane structure, wherein the membrane has a low molecular weight cut-off (allowing to eliminate or minimize the dialysis of solutes) and has an increased selectivity.
As lowering the molecular weight cut-off of the membrane results in a severe decrease in speed of operation of the device, reducing the thickness of the membrane to compensate for the reduction in speed results in an impracticably weak structure. It is therefore an aim of the present invention to provide a container comprising as membrane, a thick and strong film with a relatively high average pore diameter and number as a support for a thin layer with a relatively low molecular weight cut-off. This enables one to tune the selectivity of the composite membrane structure whilst maximizing flux.
It is a further aim of the present invention to substantially reduce dialysis which enables solutions of concentrations within the required tolerance to be obtained in a shorter period of time without the need for the precise measurement of the outer volume of water, by means of a container comprising a membrane having a first layer with very large pores which can be utilized as a support for a thin polymeric layer coated onto the surface of the first layer. The resultant reduction of dialysis also leads to considerably lower increase in external water bacteria count.
A further aim of the invention is to provide a device allowing the preparation of rehydrated solute solutions, of rehydrated blood products, of nutritional solutions, of solutions for medical purpose or of pure water into a closed container, especially in conjunction with the process of osmotically driven ultrafiltration as described in the European Patent No. 360612. It is however to be noted that the container according to the invention may be efficiently placed into flowing water (stream, river and the like) or into stagnant water (lake, pool and the like).
Description of the Invention
The invention is related to a container for the preparation of rehydrated solute solutions, rehydrated blood or blood substitutes, nutritional solutions, solutions for medical purpose or of pure water comprising a flexible semi-permeable composite membrane structure having a low molecular weight cut-off and at least one water soluble solid contained therein, which membrane comprises a flexible support layer thick enough to give strength to the membrane structure and having a relatively high molecular weight cut-off and on at least one face of the said support layer, a second layer having a relatively low molecular weight cut-off and being thin enough to allow a workable flux.
By container, it is to be understood a closed structure; for example in the form of a bag or a pouch.
By flexible membrane is understood a structure which is capable of further shaping and which is also flexible, either prior or after being brought in contact with water.
By thick enough to give strength to the membrane structure, it is to be understood that the membrane should be strong enough to prevent damages when both dry or swollen with water. By thin enough to allow a workable flux, it is to be understood that the flux should be at least 0.1 l/h.m2.bar.
The molecular-weight cut-off of the two layers to be chosen may vary within a large range.
The MWCO of the support layer is chosen in order to allow a high flux and yet to prevent the passage through the membrane of microorganisms from the outside water. One may thus select for the support layer, a film which has relatively large pores, for examples of between 2 and 20 nm of diameters. On the other hand, the MWCO of the second layer is chosen in order to prevent dialysis of low molecular weight solutes. The pore size of the support layer can thus be many times that of the second layer. Preferably, the molecular weight cut-off of the support layer is from 1,000 to 50,000 and/or the molecular weight cut-off of second layer is from 300 to 2,000.
As a matter of fact, it is to be noted that the entering flux of water is lowered by the thin second layer. The flux for a simple regenerated cellulose film is from 1.7 to 3 l/h.m2.bar and may be as low as 0.1 l/h.m2.bar for the composite film of the invention. However, surprisingly, for the composite films of the invention, as the dialysis (thus the coming out flux) is even more decreased, the resulting flux is positive and considerably increased. The relative thickness of the components of the composite membrane structure will be determined by the required flux rate and strength.
Preferably, the overall thickness of the composite membrane is from 20 to 50 &mgr;m; the thickness
Marshall Colin
Nash Darren
Salviato Jean-Yves
Sealby Lesley
Fortuna Ana
UCB S.A.
Wenderoth Lind & Ponack LLP
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