Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1985-10-28
1988-06-21
Fisher, Richard V.
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
210492, 21050038, 55158, 427245, 4283159, B01D 1304
Patent
active
047523956
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL DOMAIN
The invention is concerned with a structure which comprises at least one membrane with continuous pores, or which is formed by at least one such membrane, with said pores being particularly within the diameter range of 2 to 200 nm (nanometers) In addition, it concerns a method for the production of this structure, as well as several advantageous applications of said structure.
STATE OF THE ART
Structures with membranes that have continuous pores within a diameter range of 2 to 200 nm are, e.g., ultrafiltration membranes used in processes for the fractionation or concentration of mixtures of high-molecular organic substances with different molecular weights. Asymmetrical ultrafiltration membranes are now used in many instances for industrial and semi-industrial purposes; they are comprised of a very thin separating film which is determinative for the mass transfer through the membrane and for the selectivity of separation, and which in general is between 100 and 200 nm thick, and of a coarsely porous support layer. The separating films consist of various polymers, preferably of cellulose derivatives or polysulfones. Such ultrafiltration membranes are either phase inversion membranes or composite membranes. In phase inversion membranes, a homogeneous polymer solution is brought into contact with a precipitant, whereupon, at the polymer solution/precipitant contact surface, the membrane is formed, in which latter the coarsely porous support film is joined to the finely porous film. In composite membranes, the separating film and the support film are produced separately and joined together only subsequently.
In the known ultrafiltration membranes, the pore diameter does not have a fixed size, but the diameters of the pores vary, randomly distributed around a mean value. This behavior of the ultrafiltration membrane is characterized by its grade efficiency curve. To determine this grade efficiency curve, the R portion,which is retained by the ultrafiltration membrane during filtration, is determined, in %, for various ideal test molecules (these are spherical molecules in not charged state) with varied molecular weights (MW). The grade efficiency curve itself represents an interpolation of these test values and shows the relationship of the relative retained quantity (R) to the logarithm of the molecular weight log .rarw.(MW).
FIG. 1 shows a diagram with the grade efficiency curves for three commercially available ultrafiltration membranes, namely: Mass., U.S.A., U.S.A.
As can be seen from these grade efficiency curves, it is not possible to effect with the aid of these ultrafiltration membranes any sharp separation of molecules with slightly different molecular weights.
A further characteristic value for the performance of an utrafiltration membrane is the so-called flow rate. This is the quantity of water which flows through the membrane per m.sup.2 per hour at a set operating overpressure prevailing between both sides of the membrane. In the known phase inversion membranes, whose separating films are about 100-200 nm thick, the membrane develops considerable resistance to the water flowing through. The flow rate is higher, the higher the number of pores per unit of area of the membrane, or the lesser the effective pore depth, i.e. the length of the canals forming the pores. Additional important quality features of ultrafiltration membranes is also their chemical and/or thermal stability.
DESCRIPTION OF THE INVENTION
The invention has the task of indicating a structure which comprises at least one membrane with continuous pores or is formed of at least one such membrane, wherein said pores are within a diameter range of 1 to 8 nm and where, in its application as an ultrafiltration membrane, sharp separation can be realized, if necessary, between molecules with slightly different molecular weights, and with which ultrafiltration membrane it is furthermore possible to attain a higher flow rate than with known ultrafiltration membranes, and which has good chemical and thermal stability.
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Archives of Microbiology, 1986 by U. Sleytr et al., pp. 19-24.
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Sara Margit
Sleytr Uwe
Fisher Richard V.
Jones W. Gary
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