DE19532684A1 - Easily controlled membrane fractionation system for efficient on-line fractionation - Google Patents

Abstract

Membrane fractionation system (MFS) for sepg. macromols., particles and other microspecies in aq. or organic media has reservoirs for test and washing soln.; multichannel pumps; pipe connections; and cylindrical discs as membrane holder between cylindrical base and top plates, held together by a cap bolt. A membrane holder has (non)spiral channels on the top and a drainage system, connected to the space above the membrane of the next membrane holder, on the bottom and is fitted with a semipermeable flat membrane. In addn., each fractionation stage has a chamber between the sample flowing to the outlet and the relevant pump channel and a connection for taking samples and removing air. There are also control valve (for controlling the pressure or flow) at the inlet and outlet for the test soln. to be fractionated.

Description

The present invention relates to a device for separation or Fractionation of molecules, particles and other species in aqueous or organic media. The device is designed for applications in the analytical and macromolecular chemistry, for particle control sizes, for the fractionation of particles and macromolecules in the Environmental chemistry and analysis, for the cleaning and concentration of synthetic and natural polymers and for the specification of Components in natural aqueous media that contain solid particles.

For the fractionation of particles and soluble components in aqueous Filtration, especially membrane filtration, utilized. For this purpose, a cascade has already been used several times tionally stirred membrane filtration cells have been used. The Use of several interconnected filtration cells is therefore known. Cells of this type consist of a housing, a semi permeable filter, connecting hoses and various control instru ment. Fractionation systems of this type are, however, with a whole A number of practical disadvantages, particularly the Separation of species in the presence of solid particles very difficult e.g. B. due to inhibitory deposits on the filter top area, low flow rates, difficult control of the separation operation and due to large volumes of washing solutions that are needed for efficient Separation are required.

Conventional filtration systems are known to consist of one  Housing, corresponding holding devices for the membrane inside this housing, a fixation with screw cylinders, an entrance and output for the test solution, a stirring device (mostly based of a magnetic stirrer) and various control instruments. Main disadvantages of the previously presented fractionation systems, which consist of a Row of coupled filtration cells are a lower one Efficiency and limited applicability, especially also due to those necessary for ultrafiltration in the lower kDalton range Working pressures and their control.

Devices that come closest to the invention proposed here special ultrafiltration units that consist of reservoirs for the test and Washing solution, a multi-channel hose pump with hose connections, Control instruments, a filter pad with double spiral Flow channels, semi-permeable flat filters, as well as entrances and There are exits, which with the associated collecting vessels the outside of the ultrafiltration unit. The exits of the drainage system and the pump inputs are independent Sampling points. The devices also have one controllable distribution system for pressure registration (manometer) in the Channels. In the circuit or in the tangential flow, the sample is over the Pumped membrane membranes, connecting to the starting Collecting vessel or the solution reservoir and an abundance Safety valve leads to a side channel. In addition there is a collection vessel between the reservoir for the washing solution and the pump installed, which is connected to the circuit current.

However, there are significant disadvantages of such known filtration systems a relatively complicated control of the separation operation and some Sensitivity to solid particles in the test solution, so that its application to aqueous environmental samples and other solutions with suspended particles is not possible. In addition, the long Hose connections to considerable sorption losses substances during filtration.

The aim of the present invention is to improve the efficiency of such separation systems during an "on-line" fractionation of solution components in the presence of solid particles to improve the implementation simplify control and the areas of application for such systems expand.

description

The invention relates to that characterized in the claims Object, that is, a device for separating and fractionating Macromolecules, particles and other microspecies in aqueous or organic media.

The proposed membrane fractionation system (MFS) has the following Features: It consists of a series of directly linked Ultrafiltration stages, which are equipped with suitable membranes, and an input reservoir for the test or wash solution. The one for this MFS developed membrane supports have spiral or in the upper part also non-spiral channels and a drainage system in the lower part which leads to the membrane of the next separation stage via special channels. The sample to be fractionated is circulated or flowed through promoting tangential flow over the membrane in question, wherein a flow through each to take up the individual fractions Serves with a constant volume. At the entrance for the Test solution there is a regulating valve, also at the outlet for the final filtrate (permeate). The individual, "on-line" interconnected Separation stages that have the shape of flat cylindrical disks are through suitable plastic rings are sealed and are secured by cap screws held together from the bottom to the top separator. The test solution is led and passed through the MFS from bottom to top the individual filters according to their exclusion limit (pore size) are ordered according to the smallest pore sizes. The resulting fractions collect at the separation in the collection vessels already mentioned of the individual separation stages.  

Figure 1 shows a schematic flow diagram of the developed MFS. A cross-sectional drawing of the device is shown in Figure 2. The test solution to be fractionated is introduced from the reservoir by means of a peristaltic pump under pressure (150-200 kPa) into the first filtration stage, the solution being transported in a parallel direction over the membrane surface (tangential flow). The part of the test solution that does not penetrate the membrane returns to the reservoir. The filtrate, on the other hand, flows into the reservoir or into the tangential circuit of the next filtration stage. Here, as in the previous filtration stage, it is again passed over the membrane surface using a peristaltic pump, partially filtered or returned to the reservoir there (see Fig . 1). This filtration process is repeated at every step. In this way, as shown in Figure 1, a whole series of filtration stages (e.g. five or ten) can be connected in series. The MFS constructed in this way enables technically simple and fast "on-line" fractionation of substance mixtures, as the examined application examples demonstrate.

As can be seen in the technical drawing ( Figure 2), the MFS consists of an upper and lower part, between which the individual cylinder-shaped filtration cells, equipped with regulating valves and held together by cap screws, are arranged. The cylindrical filtration cells mentioned are equipped with connections for the inlet and outlet of the test solution circulated, with channels to the drainage system of the next filtration stage and with a chamber (rerservoir). This chamber has connections for the removal of air bubbles, for sampling during the filtration and for the previously described circulation of the fraction passed over the membrane. Rubber sealing rings placed in between are used for the external sealing of the cylindrical filtration stages. Before the MFS is put into operation, the individual filtration stages are equipped with the membranes required for the intended separation task, each equipped with a sealing ring and then, as shown in Fig. 1 or 2, placed on top of each other, with the lower and upper part already mentioned closing at the bottom or form above.

Finally, the separating stages are placed on top of each other Cylinder head screws are firmly attached to each other via the lower and upper part then those required for circulatory operation within the filtration stages Hose connections, connected via a multi-channel hose pump, produced.

The presented invention is compared to known ultrafiltration devices characterized by the following decisive advantages:

• 1. The fractionation of components is also great in solutions Contain proportions of suspended particles, possible. Hereby we the otherwise rapid clogging of ultrafiltration membranes avoided and a better, d. H. also achieved more reliable separation that is correct and accuracy of the subsequent analyzes (e.g. molecular weight Distributions of macromolecules) significantly improved.
• 2. The fractionation of solution components takes place without one Change in the chemical or gas composition of the test solution because the separation process takes place in a closed system.
• 3. The relatively small "inner" surface of the developed MFS enables it, losses of separation components caused by sorption on upper to keep the surfaces of the device system small. This makes the analytical Correctness of this separation process increased considerably.
• 4. The process control is carried out in a very simple manner through the one valve at the entrance and exit of the system. The successful use of the MFS and its special advantages could be obtained by fractionation from real ones Samples of quite different types can be detected, such as those after clearly demonstrate the following examples.

Examples of use example 1 Analysis of particles and sediment components in hydrogeological samples (e.g. "peletic matter")

A granulometric analysis of samples from natural "peletic" material was carried out in order to obtain its size fractionation in the grain ranges 250-100, 100-10, 10-2.5, 2.5-1, 1-0.45 and 0.45-0.1 µm. The fractionation was carried out using special sieves or membrane filters. It was carried out in three runs (n = 3) in the following way:
A sample of the material (50 g) was placed in a beaker (500 ml), treated with acetic acid (7%) and then deionized water was added with stirring. The suspension was then passed through the multi-stage fractionation system (equipped with membrane filters with a diameter of 145 mm). After each fractionation, the suspension fractions obtained were removed from the system, which for this purpose was rinsed with deionized water and then blown out with air. The collected fractions were dried and weighed.

The fraction values obtained in this way were certified with these Samples determined by sedimentation tests compared. Certified Values were available for the 2.5-10 µm fractions in the case of the samples 1-6, for the fractions 250-100 and 100-1 µm in the case of sample 7 and for the fraction 100-1 µm in the case of sample 8. Table 1 below summarizes this comparison for the fraction 2.5-10 µm in the case of samples 1-6 together.

The certified values in sample 7 were 18 (250-100 µm) or 82% (100-1 µm), while fractionation with the MFS 25 or 75% revealed. The result comparison in the case of Sample 8 was 98% (Sedimentation) and 91% (membrane fractionation system). Again The comparison clearly proves the correctness of the presented here  Filtration method overall as good and shows at most once a deviation of 8% from the certified value.

Table 1

Particle fractionation (fraction 2.5-10 µm, in%) using the membrane fractionation system (MFS) compared to the corresponding sedimentation experiments

Another crucial aspect is the time factor. The fractionation of suspended particle samples by sedimentation requires one Time requirement of about 3-4 days, while with the MFS only 2 hours are needed.

Example 2 Fractionation or size classification of aquatic Humic substances by filtration with the membrane fraction nation system

Aquatic humic substances (HS) are generally a complex, hardly separable A mixture of similar polyelectrolytes with different molecules sizes, (sub) structures and functionalities. The HS go in soils and aquatic environmental areas versatile interactions with the environment relevant substances. The high one is of particular interest Binding ability of the HS towards metal ions as well as organic Pollutants that are not insignificant from the molecular size distribution the HS depends. The molecular size distribution of HS is common  determined with the aid of gel permeation chromatography (GPC).

The molecular size distribution of dissolved HS can now also be determined with the analytical MFS described as follows:
10 ml samples of the dissolved HS (0.1 to 1 mg / ml HS, pH 6.0) are pumped through the MFS using a peristaltic pump (pressure: 2.0 bar) and equipped with a series of ultrafiltration membranes (nominal exclusion limits: 1, 5, 10, 50 and 100 · 10³ g / mol, 25 mm diameter), pumped with a flow of about 2 ml / h (tangential flow: 2-3 ml / min). It is then washed in the same way with 10 ml of deionized water. The HS fractions obtained in this way are rinsed out of the reservoir chambers of the individual filtration stages with 5 ml of deionized water and fed to the following determinations. Highly detectable HS determinations were carried out by means of UV / VIS spectrophotometry in the wave range from 250 to 450 nm. The following pictures 3 and 4 describe the molecular size distribution of aquatic HS from different origins (BOC 3 / 9.5 = DFG test field Bocholt, VM 4 = Venner Moor, FU 2 = Fuhrberg / Hanover, R 2 = Ruhr) as well as a comparison of the molecular size Distribution determined on the one hand by the MFS and on the other hand by conventional gel permeation chromatography (GPC).

From Figure 3 it can be seen that the molecular size distributions of aquatic HS are quite different. Figure 4 shows a fairly good agreement between the two different methods used to determine the molecular size distribution of HS. In the case of the conventional GPC, however, it becomes clear that in the case of the high molecular fractions F1 (<100 kD) and F2 (50-100 kD) it systematically produces values which are presumably due to a partial irreversible binding of the species of these fractions to the separation polymer used is attributable.

Example 3 Molar mass distribution of the polyelectrolyte poly (ethyleneimine) (PEI)

With the help of the developed MFS, molecular weight distributions for water-soluble polymers were also determined. This was investigated using the example of technical PEI (Polymin P, BASF) with an average molecular mass of 25,000 g / mol. Ultrafiltration membranes (e.g. made of polyamide or polysulfone, 47 mm diameter) with separation limits of 10, 50 and 100 g / mol were used for fractionation in the MFS:
25 ml of an aqueous PEI solution (content: 0.5% PEI) were introduced into the described MFS using a multi-channel peristaltic pump (pressure: 150 kPa) (flow rate: 10 ml / h, tangential flow: 5 ml / min) and then with 25 ml deionized water. The fractions obtained in this way were rinsed with 5 ml of deionized water from the MFS and then determined spectrophotometrically (at 240 nm, spectrophotometer: Varian Cary 1/3). Fractionation took about 3 hours. According to the spectrophotometric determinations, 25.6% of the PEI was for the <10 kDalton fraction, 43.2% for the 10-50 kDalton fraction, 18% for the 50-100 kDalton fraction and 13.2% for the <100 kDalton fraction. The mass balance showed practically no PEI losses (PEI recovery rate: <98%).

Claims (2)

1. Membrane fractionation system (MFS) for the separation of macro molecules, particles and other microspecies in aqueous or orga media, equipped with reservoirs for test and washing solutions, with multi-channel pump, with hose connections, with a cylinder shaped bottom and top plate, between which cylindrical discs are arranged as a membrane holder and together by cap screws be kept, especially equipped with those already mentioned cylindrical discs as membrane holders in their upper part spiral or non-spiral channels and in their lower part Drainage system included, which corresponds to the space above the membrane of the next cylindrical disc is connected, as well as equipped with semipermeable flat membranes. The equipment of this MFS includes in addition, a chamber at each fractionation level, which is between the Outlet of the sample flowing in the circuit over the membrane and the associated associated pump channel is arranged and also the connections for the Includes sampling and air removal. At the entrance and exit of the MFS are also regulating valves (for the purpose of pressure or flow Regulation) for the test solution to be fractionated. 2. Membrane fractionation system according to claim 1, in which the frak tioning solution from bottom to top.