Dynamic filter separator

Abstract: An apparatus and a method for separating a suspension into a filtrate and a concentrate. There is provided a separation means and a method in which partial filtrates are collected as a plurality of filtrate streams in a plurality of parallel filtrate chambers. The filtrate chamber is divided into several partial filtrate chambers, each of which is connected to a different portion of a partially permeable wall or membrane and receives that part of the filtrate passing therethrough. Also, a relative motion is induced between the suspension and the wall or membrane by a rotating part, thus preventing clogging of the membrane. Furthermore, sensors are provided in the partial filtrate chambers, permitting more information about a dynamic separation process to be obtained.

Description: The invention relates to an apparatus and a method for separating a feed fluid, particularly a suspension into a less concentrated or even pure phase (filtrate fluid) and a more concentrated phase (concentrate fluid). In areas such as biotechnology, waste water treatment, pharmacy, medicine and the beverage industry, it is a frequent problem to separate solid particles from a feed fluid, such as enzymes or yeast in an aqueous solution, blood in plasma or pulp from juice, etc. The EP-A-0 238 335 discloses an apparatus for fractionating a cell suspension having a disc like rotating body. Previously known dynamic filter separators work with a two chamber system. The feed fluid is impelled in a first chamber, called concentrate chamber which is separated from a second chamber, the filtrate chamber, by a partially permeable wall (semi-permeable membrane). In the second chamber the filtrate is collected from the whole plane of the membrane. Said concentrate chamber is connected to a feed fluid entering means and a concentrate fluid exiting means, the filtrate chamber is connected to a filtrate fluid exiting means. Such a filter is called dynamic, when a relative motion of the suspension in the concentrate chamber along the membrane is induced by any means, for example a rotatable disc. Thus, clogging of the membrane pores is avoided or at least diminished. In this state of the art the effect of different degrees of separation of the suspension at different locations at the membrane had not been taken into account. Any inhomogeneous behavior of the separation process due to e.g. parameters of the feed fluid such as pressure, temperature, concentration or velocity in the concentrate chamber has not been considered. One of the objects of the invention is to provide a dynamic filter separator and a dynamic filtration method with improved separation characteristics. A further object of this invention is to provide a dynamic filter separator permitting obtaining more information about a dynamic separation process. A yet further object of this invention is to provide a dynamic filter separator as a tool for the development of a dynamic filter separator and process specifically adapted to a particular separation problem. The invention provides a separator and method in which partial filtrate fluids are collected as a plurality of filtrate fluid streams in a plurality of separate parallel filtrate chambers. The filtrate chamber is divided into several partial filtrate chambers, each of them connected to a different portion of the partially permeable wall or membrane and receiving that portion of the filtrate which passes therethrough. Other features, modifications and applications of the separator and method of this invention are described in the claims. This multi-chamber system provides a different kind of separation for a partial filtrate fluid in comparison to the mixed filtrate fluid that is received by a two-chamber system. Partial filtrate fluids then can e.g. differ in the degree of separation. Thus, the feed fluid is separated differentially into a multitude of filtrate fluids with generally different concentration, flow rates or other properties being different from one partial filtrate stream to the next. There are several advantages to this differential separation. A higher degree of separation for a partial stream can be obtained. The separation process itself can be investigated by analyzing the degree of separation depending on the location at the membrane where the filtrate fluid is connected as well as depending on other parameters, e.g. geometrical parameters (gap shape, surface structure of rotatable element). It is preferred to install one or more sensors at the filtrate and/or concentrate chambers in order to monitor physical or chemical properties of the fluids, such as concentration, temperature, pressure or flow rate depending on the location in said chambers. In this case a differential separation process does not have to be run by trial and error but can be controlled and predetermined systematically. It is also possible to provide membranes with different properties for different partial filtrate chambers, such that the membrane is composed of a plurality of portions of different membranes. Therefore, the possibility of testing different membranes at the same time arises in order to find a membrane that meets best the special demands of the specific case. Especially for testing and development purposes it is advantageous to build the housing of the filter separator of at least two parts, such that relevant parts (membrane, relative motion inducing means) for the separation process can easily be changed. Figures 1 and 2 show a preferred embodiment of a differential dynamic filter separator, Fig. 2 being a cross-sectional view along line II-II of the separator of Fig. 1. An apparatus according to Figures 1 and 2 shows a ring channel differential rotational shearing gap filter separator. A feed fluid is fed into the concentrate chamber 4, which is formed by lid 4a and bottom 4b, via the central feed fluid entering means 1, a hollow shaft. In the concentrate chamber 4 there is installed a rotatable disc 11. It forms a gap 12 with the semi-permeable membrane 6. Rotating the disc 11 induces a relative motion of the feed fluid in the gap 12 along the membrane 6, one of the possible effects being in to avoid or diminish clogging of the membrane pores. The filtrate chamber 5 of the system is divided into several partial filtrate chambers 5 1 to 5 n which are arranged in this preferred embodiment as concentric rings in the bottom 4b around the rotational axis 10 of the rotatable disc 11. The suspension that was fed near the middle of the rotatable disc 11 is led to the outer edge of the concentrate chamber 4. The feed fluid is concentrated each time when passing a ring channel with a membrane and a connected partial filtrate chamber. The different filtrate fluids which are collected in said ring channels 5 are drained by filtrate exiting means 3. Thus a differential separation process occurs. The different collected filtrate fluids can have different properties, e.g. different concentration of particles. The remaining concentrate fluid is expelled by the concentrate exiting means 2. In order to exchange the rotatable disc and the membrane easily the housing of the filter separator is horizontally divided into two parts. Preferably, these two parts are connected by bolts 8 and a sealing 7. In a preferred embodiment of this invention sensors 13 are provided in each partial filtrate chamber 5 1 , ... , 5 n or the outlet conduit 3 thereof. These sensors 13 may e.g. be flow rate sensors, concentration sensors, pH sensors, viscosity sensors, pressure sensors. The filter separator may also in a further embodiment have radial sectors of membrane portions with different properties instead of the ring channel arrangements of Figure 1. Several membranes can thus be installed and tested under the same circumstances. The following two examples illustrate the invention. Example 1 In the differential filtration apparatus as described above four different baker's yeast solutions were employed to determine the separation quality of a membrane. The flux in liters per hour for the four different solutions at the seven different ring channels have been determined and the results have been plotted in Figure 3. As can be seen, the flux increases from the inner ring channel 5 1 to the outer ring channel 5 n . The dependency is particularly strong for the more diluted solution of 5 percent, while the other concentrations of 20 weight percent, 60 weight percent and 80 weight percent, respectively, show a smaller, but still significant dependency of the flux upon the radius r of the ring channel. The filter membrane used for this experiment was a 0.2 micrometer nominal nylon membrane, marketed under the trademark "Ultipor®" by Pall Corporation. Example 2 In this example a solution of homogenized E. coli was used in the same apparatus. The membrane employed was a 0.2 micrometer nominal PVDF membrane, commercially available from Pall Corporation under the trademark "Fluorodyne®". Figure 4 shows the dependency of the protein transmission plotted on the ordinate vs. the average radius r m of the ring channel in mm ranging from 25 to 85 mm. The corresponding local velocity v R of the rotor is also shown in this Figure 4. This local velocity above the membrane portion covering the respective ring channel is between about 6 and about 20 m/sec. The plotted data shows that the transmission rate, which is the ratio of protein concentration in the filtrate to the protein concentration in the concentrate ranges from about 25 percent to 100 percent. Test runs have been carried out with a PVDF membrane of 0.2 micrometer (commercially available under the trademark "Fluorodyne II®" from Pall Corporation) under 200 mbar over 1.5 hours (crosses in the diagram) and with a 0.2 micrometer nylon membrane (commercially available under the trademark "Bio-inert II®" from Pall Corporation) under a pressure of 700 mbar over 4.5 hours (dots in the diagram). Attention is drawn to the fact that in this example the purpose was to determine how efficiently the membrane passes the homogenization products, i.e. the smaller protein molecules. For this test a transmission of 100 percent is desirable. The results clearly demonstrate that from above roughly 55 mm average radius of the channel the transmission is 100 percent. Further, it is pointed out that the above examples are not about examining protein transmission globally, but for a special protein in particular.

Claims: A dynamic filter separator comprising a housing; a supporting structure having one essentially plane surface carrying a partially permeable wall (6) separating the space within the housing of the dynamic filter separator into a concentrate chamber (4) and a filtrate chamber (5); a feed fluid entering means (1) and a concentrate fluid exiting means (2) connected to said concentrate chamber (4); a means (11) inducing a relative motion between the feed fluid in said concentrate chamber (4) and said partially permeable wall (6) with at least a component parallel to the partially permeable wall (6), a filtrate fluid exiting means (3) connected to said filtrate chamber (5), characterized in that said filtrate chamber (5), which is connected via said partially permeable wall (6) on said one essentially plane surface with said concentrate chamber (4), is divided into a plurality of partial filtrate chambers (5 1 , 5 2 , ..., 5 n ) each collecting filtrate fluid from a different portion of said partially permeable wall (6) through a respective access in said supporting structure, said accesses being located in said one plane. The dynamic filter separator according to claim 1, wherein said means (11) inducing a relative motion is a rotatable part adjacent to said partially permeable wall (6) such that a gap (12) is formed between said rotatable part (11) and said partially permeable wall (6). The dynamic filter separator according to claim 2, wherein said rotatable part (11) is a rotatable, preferably circular disc. The dynamic filter separator according to claims 2 or 3, wherein said feed fluid entering means (1) is connected to said concentrate chamber (4) near the rotational axis (10) of said rotatable part (11) and disc, respectively. The dynamic filter separator according to any of the preceding claims, wherein said housing of the dynamic filter separator is composed of at least two parts arranged and constructed such that the housing can be easily opened such that said partially permeable wall (6) and/or said means (11) inducing said relative motion are easily exchangeable. The dynamic filter separator according to any of the preceding claims, wherein said portions of said partially permeable wall (6) have different properties. The dynamic filter separator according to any of the preceding claims, wherein said portions of said partially permeable wall (6) are concentric annular rings. The dynamic filter separator according to any of the preceding claims, wherein said portions of said partially permeable wall (6) are radial sectors. The dynamic filter separator according to any of the preceding claims, wherein at least one sensor (13) in at least one of said partial filtrate chambers (5 1 , 5 2 , ...., 5 n ) for determining and optionally monitoring at least one property of said filtrate fluid is provided. The dynamic filter separator according to any of the preceding claims, wherein at least one sensor (13) for determining and optionally monitoring at least one property of said concentrate fluid is provided. A method for separation employing a dynamic filter separator according to any of the preceding claims said method being characterized by a) feeding said feed fluid into said concentrate chamber (4) with a relative motion between said feed fluid and the partially permeable wall (6) imparting on said feed fluid at least a component of its movement parallel to the partially permeable wall (6); b) collecting separate streams of filtrate fluid in partial filtrate chambers (5 1 , 5 2 , ...., 5 n ) from different portions of said partially permeable wall (6). The method in according to claim 11 further comprising measuring at least one of the properties flow rate (cm 3 /second), density, composition, concentration, pressure of said filtrate fluid of said partial filtrate chambers (5 1 , 5 2 , ...., 5 n ), etc. The method according to claim 11 or 12 further comprising withdrawing concentrate fluid from said concentrate chamber (4). The method according to one of the preceding method claims wherein said means inducing a relative motion comprises a rotatably arranged element (11) forming a gap (12) between said element (11) and said partially permeable wall (6), said disc (11) being rotated at a defined speed. The method according to one of the preceding method claims, further comprising the steps of changing at least one parameter of said dynamic filter separator and/or of said method, and carrying out at least one measurement of a parameter of said separation method prior to and after said change.

Inventors: MEISTER MICHAEL, RANDHAHN HORST DR, VOGELMANN HARTMUT DR, MEISTER, MICHAEL, RANDHAHN, HORST, DR., VOGELMANN, HARTMUT, DR.
Applicants: PALL CORP, PALL CORPORATION
Application year: 1993
Main classification: B01D29
IPC codes: B01D61, B01D65, B01D63, B01D29