Method for the separation of substance mixtures

The invention relates to a method for separating mixtures of substances according to the principle of a simulated fluidized bed, with mixture and desorbent being added and pure substances of the separated mixture being withdrawn in a controlled time sequence at several points of the packed bed.

In the known method of this type, as disclosed by US Pat. No. 5,156,736, such a simulated fluidized bed is implemented. The content of this document is hereby expressly incorporated into the present description by reference. In this known design it is provided that a fluidized bed is simulated in a continuous absorption bed in which the sorption carrier is held by a distributor for injecting liquid or for collecting product is arranged at several predetermined points, these distributors cyclically for feeding in the mixture or desorbent to be separated or for removing the pure substances after separation with the associated feeding line or connected to the associated process. The separation principle is that the entire column is flowed through by carrier fluid, which circulates via an external line. The separation of the individual substances is based on the different sorption behavior on the carrier that builds the bed. Due to the cyclical application of desorbent in between and the cyclical removal of the cleaned products, the sequence of a fluidized bed is simulated, whereby the local movement of a fluidized bed is simulated by the chronological sequence.

In the case of products in which the sorption capacity of the pure substance on the carrier substance is high and thus the pure product is drawn off via the distributor via which the product mixture to be separated was previously applied in the previous step, it occurs in each step - to the extent that is due to the geometry of the distributor given volume - to considerable contamination of the pure product by those substances that are still present in the substance mixture in addition to the pure product.

The invention is therefore based on the object of creating a method of the type mentioned at the outset in which such impurities are avoided.

According to the invention, this is achieved by flushing the associated apparatus or lines and / or distribution device with the desorbent for the pure product after each mixture application, with the amount of mixture in the apparatus or line and / or distributor being flushed with the pure liquid the bed is pressed. The consequence of this is that all of the material introduced is fed to the separation and, moreover, only pure liquid remains in the apparatus, the distributor or the lines, which eliminates contamination of the pure product, which is withdrawn in the next step. Furthermore, the fact that the total amount of mixture added is always subjected to the separation also counteracts any losses. Above all, this also results in a higher degree of purity in the end product. The cleaning always takes place immediately after the substance mixture has been added, u.zw. at the distributor that was used to feed the mixture in this step.

The amount of cleaning liquid can advantageously be regulated via the mass flow rate or the volume, which ensures that on the one hand the entire volume of the mixture is introduced into the column, but also prevents too much pure liquid from entering the chromatographic concentration profile on the other hand.

An exemplary embodiment of the subject matter of the invention is described in more detail below, only one embodiment with four zones being shown for the sake of simplicity. In the same way, systems with a multiple of four can also be constructed in an analogous manner and operated according to the invention.

In Fig. 1, 1 is a separation column consisting of a continuous column which is filled with an ion exchange resin, denotes, from the bottom of which a circulation line 2 leads away, which opens into the same at the top of the column 1 again u.zw. Via a distribution device 3. With 4, 5, 6 further distribution and collection devices are provided which reach into the resin of the bed. These distribution devices serve on the one hand to introduce the mixture of substances to be separated and, with a corresponding time delay, also to remove cleaned material again. The sequence control takes place via a special valve control, which is shown schematically in FIG. 1. Fig. 2 shows the respective task or withdrawal point according to a scheme,

AT 41 2 258 Β according to which the product is added or withdrawn. The corresponding media codes PFH, PG, WT, PF mean: PFH addition of the mixture, PG removal of the weakly adsorbed component, WT addition of desorbent, PF removal of the strongly adsorbed component.

In the example of glucose / fructose separation, the input streams are the equilibrium syrup (PFH) and the water (WT) which forms the desorbent or eluent, the output streams are the raffinate (PG), i.e. the process stream enriched in glucose and the extract (PF) , so the fructose-rich deduction.

In FIG. 3, the diagram shows the concentration of the individual substances in relation to time, the right abscissa containing the proportion of fructose in dry matter. The column is shown schematically under each diagram, the arrows indicating where the material or desorption liquid is added and the product is withdrawn. (PG means glucose withdrawal, PFH means abandonment of mixture, PF denotes withdrawal of fructose and WT means abandonment of desorbent).

While the equilibrium syrup is being abandoned, the fructose-depleted one synchronously becomes depleted

Medium drawn off at a distribution system which is further down in the direction of flow (raffinate). This is possible because the fructose is bound more strongly to the calcium-laden resin than the glucose and the oligosaccharides (ligand affinity) that occur in smaller quantities. The fructose enriched in this way is later regenerated from the resin using water as an eluent. This is not done temporally, but shifted spatially in the column above.

The control of the chromatographic system is coordinated via a computerized process control system (PCS). Both the injection of the sugar mixture PFH and the eluent WT and the withdrawal of the sugar solutions enriched with glucose PG and fructose PF take place simultaneously. All of these process streams have different values, but are related to one another. These values ​​are controlled by the PCS system.

Since these feed and take-off points are connected downstream of the moving components on the column, this system is called a simulated moving bed. A series of on / off valves, the action of which is also precisely timed by the PCS system or a sequence of steps, is used to determine when and where to give up or take off.

The countercurrent flow of the resin bed is simulated by changing the location of the inlet and outlet points over time. These points are switched on in the direction of the movement of the individual components to be separated. This is carried out at constant time intervals, generally referred to as step time. As already mentioned above, the flows must be coordinated in terms of quantity in order to avoid an increase in pressure in the columns.

Likewise, the amount of dissolved substances in the inlet must correspond to the sum of the dissolved substances in the outflow streams in order to keep the concentrations in the system constant so that a steady state is established.

In order to achieve higher purities in the product, it is not pushed in and withdrawn during the entire step time, but only during a shorter period of time, the so-called feed time. In this way, narrower sugar fractions can be cut from the concentration profile. After the pushing in and pulling off has been completed, the chromatographic system only circulates in order to track and switch the inflow and outflow points to the migrated sugar profile after the step time has elapsed. A new step begins. Although the injection and withdrawal are interrupted sequentially, it is a continuous process, since the chromatographic separation works continuously. The concentration profiles of the sugars in the column consequently move continuously.

The downstream connection of these delivery and acceptance points must be precisely coordinated with the movement of the individual components in the chromatographic system. In order to position this downstream connection of the inflow and outflow points at the correct time and place of the concentration profile in the column, it is necessary to know this concentration curve exactly. For this reason it is necessary to track the glucose and fructose concentration by means of inline / online measurement. These values ​​are transferred simultaneously to the PCS system. In this way it is possible to display a current concentration profile at all times. By entering parameters such as the displacement volume or the various time parameters, it is possible to control the process. By entering various process parameters

AT 41 2 258 B the ongoing process can then be influenced and thus optimized.

In Fig. 3, the concentration curves of the components (glucose and fructose), the

Total dry matter course and the course of purity (content of fructose in total dry matter) plotted against time. The bars below symbolize the column with its individual zones. This combined display shows the position of the individual components in the column at a specific time. The arrows on the relevant distributor show the entry or discharge positions of a specific process stream in relation to the current step.

The mobile phase is moved from top to bottom in the column (FIG. 1) in the chromatogram io (FIG. 3) the movement of the mobile phase from right to left is shown. The sugars move in the same direction at different speeds.

The sequence starts in step 1 as soon as the zone with the highest dry matter content has reached the top of the column. The injection phase begins with the injection of the substance mixture PFH at the head of the column (see Fig. 2, top line, 1st column), for this purpose valve XV11 (see Fig. 1) is opened. All other valves on the valve cross of the head distributor (3) remain closed.

At the same time, the fraction enriched with glucose is drawn off at the central distributor (4) with PG by opening valve XV24. This takes place in that zone of the chromatogram in which the glucose is enriched (Fig. 3).

The desorbent (WT) is fed in synchronously at the central distributor (5) and the fructose-rich fraction (PF) is drawn off at the central distributor (6). For this purpose the valves XV 32 and XV 43 are opened. The opening of all the valves mentioned takes place synchronously. After the end of the injection phase, all of the above-mentioned valves are closed. When the push-in phase of the 2nd step is reached (see Fig. 3, 2. Step) the process streams flow as shown in the flow chart (Fig. 2) in column 2.

In this way, the individual steps of the positions of the components are followed up until they have passed through the entire chromatographic system, consisting of the sorption bed 1 and the circulation line 2.

In the present description, the system consists of 4 zones which are passed through after 4 steps. However, as already mentioned, the system can consist of n times 4 zones, for

Throughout a cycle, n times 4 steps are necessary, n are all whole positive numbers (1, 2, 3, ...).