Device for Purifying a Product and Method for Purifying a Product

Abstract

A device for purifying a product by crystallization includes: a feed unit having a solution in which the total product concentration is substantially completely dissolved or a suspension with the total product concentration; a crystallization unit in which the product crystallizes and forms a solids content; a separation unit in which the crystallized product is separated from the solution or suspension; a temperature control unit for controlling temperature at least in the feed unit and/or the crystallization unit; and a control and evaluation unit that determines the total product concentration and/or the concentration of the solids content and/or the concentration of the dissolved product content and/or the concentration of an impurity content, taking into account the measured values of connected temperature sensors and of connected impedance sensors.

Claims

1. A device for purifying a product by means of crystallization, wherein the product is produced by a chemical method and wherein the product has an impurity content, comprising: a feed unit with a solvent, wherein the product is fed to the device via the feed unit during operation, so that in the feed unit there is a solution in which the total product concentration is substantially completely dissolved, or a suspension with the total product concentration; a crystallization unit, in which the product crystallizes during operation and thus forms a solids content, wherein a further content of the product is present as a dissolved product content; a separation unit, in which the crystallized product is separated from the solution or suspension; a temperature control unit by means of which the temperature can be controlled at least in the feed unit and/or the crystallization unit; and further comprising a control and evaluation unit; wherein a temperature sensor and an impedance sensor are arranged in each case at at least two locations of the device; wherein the temperature sensors and the impedance sensors are connected to the control and evaluation unit; and wherein the control and evaluation unit is designed such that, during operation, it determines the total product concentration and/or the concentration of the solids content and/or the concentration of the dissolved product content and/or the concentration of the impurity content, taking into account the measured values of the temperature sensors and of the impedance sensors.

2. The device according to claim 1, wherein the separation unit is connected to the feed unit via a return unit, so that, during operation, the solution or the suspension flows through the feed unit into the crystallization unit into the separation unit and through the return unit back into the feed unit.

3. The device according to claim 1, wherein a first impedance sensor and a first temperature sensor are arranged in the feed unit: wherein a second impedance sensor and a second temperature sensor are arranged in the crystallization unit; and wherein a third impedance sensor and a third temperature sensor are arranged in the return unit, if present.

4. The device according to claim 1, wherein the control and evaluation unit carries out a method during operation, the method including the following steps: a preparatory step, in which the relationship between the electrical impedance of the solution or the suspension and the temperature and/or the total product concentration in the solution or the suspension and/or the solids content and/or the impurity content is captured; wherein a calibration matrix is determined from the captured relationship; and wherein, during operation of the device, the following steps are carried out; a feed step, in which the product is fed to the feed unit, wherein the product is placed in solution or suspension in the feed unit, or wherein the product is fed in solution or suspension to the feed unit; wherein the temperature in the feed unit is adjusted such that the solution or suspension is in an undersaturated state; starting crystallization in a crystallization step by bringing the solution or suspension to a supersaturated state, by adjusting the temperature to a target temperature, wherein the total product concentration in the crystallization unit is the sum of the crystallized solids and the dissolved product content; capturing the electrical impedance and temperature at at least two locations of the device in an impedance measurement step; determining the total product concentration and/or the solids content and/or the dissolved product content and/or the impurity content in an analysis step from the electrical impedance the measured temperature, and the calibration matrix.

5. A method for purifying a product with a device including a feed unit with a solvent, wherein the product is fed to the device via the feed unit during operation, so that in the feed unit there is a solution in which the total product concentration is substantially completely dissolved, or a suspension with the total product concentration, a crystallization unit, in which the product crystallizes during operation and thus forms a solids content, wherein a further content of the product is present as a dissolved product content, a separation unit, in which the crystallized product is separated from the solution or suspension, a temperature control unit by means of which the temperature can be controlled at least in the feed unit and/or the crystallization unit, and further comprising a control and evaluation unit, wherein a temperature sensor and an impedance sensor are arranged in each case at at least two locations of the device wherein the temperature sensors and the impedance sensors are connected to the control and evaluation unit, and wherein the control and evaluation unit is designed such that, during operation, it determines the total product concentration and/or the concentration of the solids content and/or the concentration of the dissolved product content and/or the concentration of the impurity content, taking into account the measured values of the temperature sensors and of the impedance sensors, wherein the product is produced by a chemical method, and wherein the product has an impurity content, the method comprising: in a preparatory step, the relationship between the electrical impedance of the solution or the suspension and the temperature and/or the total product concentration in the solution or the suspension and/or the solids content and/or the impurity content is captured; wherein a calibration matrix is determined from the captured relationship; and wherein, during operation of the device, the following steps are carried out: in a feed step, the product is fed to the feed unit, wherein the product is placed in solution or suspension in the feed unit, or wherein the product is fed in solution or suspension to the feed unit; wherein the temperature in the feed unit is adjusted such that the solution or suspension is in an undersaturated state; starting crystallization in a crystallization step by bringing the solution or suspension to a supersaturated state, by adjusting the temperature to a target temperature, wherein the total product concentration in the crystallization unit is the sum of the crystallized solids and the dissolved product content; capturing the electrical impedance and temperature at at least two locations of the device in an impedance measurement step; determining the total product concentration and/or the solids content and/or the dissolved product content and/or the impurity content in an analysis step from the electrical impedance, the measured temperature, and the calibration matrix.

6. The method according to claim 5, wherein for determining the total product concentration and/or the solids content and/or the dissolved product content and/or the impurity content, limiting conditions resulting from the arrangement of the temperature sensors and the impedance sensors in the process are additionally taken into account.

7. The method according to claim 5, wherein the permittivity and/or the electrical conductivity of the solution or the suspension is determined with the electrical impedance.

8. The method according to claim 5, wherein the crystal growth is monitored after the onset of crystallization.

9. The method according to claim 5, wherein the impurity concentration in the mother liquor is monitored; wherein a limit value for the impurity concentration is stored in the device; and wherein solvent is replenished into the feed unit or the solvent is at least partially replaced if the impurity concentration exceeds the limit value.

10. The method according to claim 5, wherein the product is replenished in such a way that the total product concentration in the solution or in the suspension remains substantially constant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] There is now a large number of possibilities for designing and further developing the device according to the invention and the method according to the invention.

[0050] Reference is made to the following description of preferred embodiments in conjunction with the drawings.

[0051] FIG. 1 illustrates a schematic embodiment of a device for purifying a product.

[0052] FIG. 2 illustrates an arrangement for impedance measurement.

[0053] FIG. 3 illustrates a device for determining the calibration matrix product.

[0054] FIG. 4 illustrates a measuring point matrix for characterizing the process.

[0055] FIG. 5 illustrates a correlation between the conductivity and the total product concentration.

[0056] FIG. 6 illustrates a correlation between permittivity and total product concentration.

[0057] FIG. 7 illustrates a model for determining the desired parameters solids content β, dissolved product content γ and impurity content δ.

[0058] FIG. 8 illustrates a relationship between temperature, conductivity and permittivity.

[0059] FIG. 9 illustrates an embodiment of a method for purifying a product.

[0060] FIG. 10 illustrates a further embodiment of a method for purifying a product.

DETAILED DESCRIPTION

[0061] FIG. 1 shows a schematic embodiment of a device 1 for purifying a product, wherein the product is produced by means of chemical process engineering, and thus has an impurity content δ due to production.

[0062] The device 1 comprises a feed unit 2, wherein the feed unit 2 comprises a solvent, and wherein, during operation, the product is fed to the device 1 via the feed unit 2, such that in the feed unit 2 there is a solution in which a total product concentration α is substantially completely dissolved, or a suspension having the total product concentration α.

[0063] In addition, the device 1 comprises a crystallization unit 3 in which the product crystallizes during operation to form a solids content β, wherein a further content of the product is present as a dissolved product content γ.

[0064] Furthermore, the device 1 has a separation unit 4 in which the crystallized product is separated from the solution or suspension.

[0065] The separation unit 4 is connected to the feed unit 2 via a return unit 5, so that, during operation, the solution or the suspension is fed back to the feed unit 2. In addition, the crystallized part of the product is separated from the solution or the suspension in the separation unit 4.

[0066] A cyclic system is thus shown overall, in which the solution containing the product to be purified or the suspension containing the product to be purified flows through the device 1.

[0067] The temperature in the feed unit 2 and in the crystallization unit 3 and in the return unit 5 is controlled by a temperature control unit 6. During operation, the temperature in the feed unit 2 is controlled in such a way that the product is completely dissolved or finely dispersed. In the crystallization unit 3, the temperature is controlled in such a way that crystal formation and crystal growth of the product take place. In the return unit 5, the temperature is typically controlled such that the product is completely dissolved at the outlet to the feed unit 2.

[0068] Furthermore, the device 1 comprises a control and evaluation unit 7.

[0069] A temperature sensor 8 and an impedance sensor 9 are arranged in the feed unit 2, in the crystallization unit 3 and in the return unit 5, respectively, which determine the temperature and the impedance in the feed unit 2, the crystallization unit 3 and in the return unit 5, respectively, during operation.

[0070] The quantity to be determined or monitored, total product concentration α and/or solids content β and/or dissolved product content γ and/or impurity content δ, can be determined during operation from the measured values of impedance and temperature.

[0071] Due to the presence of the plurality of temperature sensors 8 and impedance sensors 9, in particular due to their arrangement in the process, further conditions can also be created which can be used to determine the previously mentioned parameters. By permanently determining these parameters, the crystallization process can be monitored particularly advantageously and controlled efficiently.

[0072] FIG. 2 shows an example of an arrangement for measuring the impedance of a liquid.

[0073] The parallel arrangement of a capacitance C and an electrical conductivity G is shown.

[0074] The electrical impedance Z is determined via the admittance Y. It holds true:

[00001]$Y=\frac{1}{Z}\approx G+j\omega C\approx \frac{1}{k}\left(\sigma +j\omega {\epsilon }_0{\epsilon }_r\right),$

[0075] where σ is the electrical conductivity and ε.sub.r is the permittivity.

[0076] Thus, both the electrical conductivity σ and the permittivity ε.sub.r of the medium can be determined from the measurement of the impedance.

[0077] FIG. 3 shows the arrangement of a device for determining the calibration matrix of a product, wherein the product to be purified is arranged in a solvent in a container 13.

[0078] The device comprises an impedance sensor 9, which is designed as a coaxial sensor in the embodiment shown, for detecting the electrical impedance of the solution, and a temperature sensor 8, which is designed as a Pt 1000 or as a Pt 100 in the embodiment shown. Both sensors 8,9 are immersed in the solution or suspension. The impedance sensor 9 is connected to a vector network analyzer 14, and the temperature sensor 8 is connected to a multimeter 15. The network analyzer 14 and the multimeter 15 are in turn connected to a computer 16, which determines the calibration values based on the measured impedance.

[0079] FIG. 4 shows the solubility curve 17 of a product in a liquid medium. Knowledge of the solubility curve 17 of the product in the selected solvent is required in order to be able to deduce, on the basis of the measured temperature and the total product concentration α determined from the characteristic, whether and in what concentration the product is present in crystalline form in the suspension.

[0080] The solubility curve 17 of a product in the selected solvent is usually known and can therefore be taken as given. Above the solubility curve 17, the product is in the supersaturated state 18. Below the solubility curve, the product is in the undersaturated state 19. With higher total product concentration α, the temperature also increases to produce the supersaturated state 18.

[0081] In addition, measuring points are entered in the coordinate system, via which the system is characterized in a preparatory step.

[0082] The influence of the temperature on the electrical impedance without product concentration can be determined via the measuring points 20 along the x-axis. Knowledge about the influence of temperature on the electrical impedance in solution, i.e. in the fully dissolved state can be determined using the measuring points 21 in the undersaturated region for the same product concentrations at different temperatures. Knowledge about the influence of temperature on the electrical impedance of the product in suspension can be determined using the triangular measuring points 22, which have different temperatures for the same product concentration. In addition, knowledge of the effect of product concentration on electrical impedance can be obtained from the cross-shaped measuring points 24.

[0083] Furthermore, all characterizing measuring points are determined for different impurity contents δ, thus creating a multi-dimensional measuring point matrix for characterizing the system.

[0084] The relationships established by means of the measuring points 20, 21, 22, 23, 24 shown in FIG. 4 can be represented in the form of various characteristic curves and stored in the control and evaluation unit 7. FIGS. 5 and 6 show, as examples for an organic product, the dependence of the conductivity σ on the total product concentration α (FIG. 5) and the dependence of the permittivity ε.sub.r on the total product concentration α (FIG. 6). In each case, the onset of crystallization is marked by the vertical line. It can be seen that, in contrast to conductivity, permittivity changes more strongly dependent on total product concentration with onset of crystallization. From the slope of the permittivity, therefore, a statement can be made about the presence of crystals in the suspension.

[0085] FIG. 7 shows a model for determining the desired parameters solids content β, dissolved product content γ, and impurity content δ based on the measured impedance Z.sub.1, Z.sub.2 to Z.sub.n, and the corresponding temperatures T.sub.1, T.sub.2 to T.sub.n at n measuring points.

[0086] The measured electrical impedance at each measuring point exhibits a dependence on the total product concentration α, impurity δ, and temperature T. If the complex-valued electrical impedance is broken down into its real and imaginary parts, these also exhibit dependencies on α, δ and T, respectively. By linking at least two measuring points while simultaneously taking into account the temperature measured at these measuring points and adding a process model 26 generated from prior process knowledge 25, the target parameters ρ, γ and δ can be determined from the values of conductivity and permittivity.

[0087] By using more than two measuring points, the accuracy of the determined target parameters can be further improved, since, for example, measurement errors can be reduced by averaging or plausibility checks.

[0088] FIG. 8 shows the dependence of the electrical conductivity and the permittivity of a substance in a non-aqueous solution or suspension on the temperature. Here, for an initially completely dissolved substance, which was present in solution at 20% w, the temperature was reduced from 60° C. to −20° C., resulting in crystallization of the substance at approx. 44° C. The onset of crystallization can be seen by a jump in the curve of electrical conductivity and permittivity. The curve also shows that the permittivity gradient changes after the onset of crystallization but remains linear, while the electrical conductivity gradient varies with respect to the mathematical sign.

[0089] When an approximately constant temperature is reached in the crystallization unit, the permittivity slowly approaches a final value. In this phase, there is a slow crystal growth, in which it is not the amount of crystalline material increases, but the crystal size itself. Based on this fading curve, an operator of the process can decide at which point the crystallization process is technically complete and the desired amount and size of crystals is present.

[0090] FIG. 9 shows a first embodiment of a method 27 for purifying a product with a device 1, wherein the device 1 is designed as described in FIG. 1, wherein the product is produced by a chemical process, and wherein the product has an impurity content δ.

[0091] In a preparatory step 28 of the method 27, the relationship between the electrical impedance of the solution or suspension and the temperature and/or the product concentration α in the solution or suspension and/or the degree of crystallization p and/or the impurity concentration δ is captured.

[0092] From the acquired relationship, a calibration matrix is determined 29 by which the desired parameters are determined during operation.

[0093] During operation of the apparatus, the following steps are carried out:

[0094] In a feed step 30, the product is fed to the feed unit, wherein the product is placed in solution or suspension in the feed unit, or wherein the product is fed in solution or suspension to the feed unit.

[0095] The temperature in the feed unit is thereby adjusted such that the solution or the suspension is in an undersaturated state.

[0096] In a crystallization step 31, crystallization is stimulated by adjusting the temperature, wherein the total product concentration α is the sum of the recrystallized solid β and the dissolved product content γ.

[0097] In an impedance measurement step 32, the electrical impedance and temperature are measured in at least two locations of the device.

[0098] In addition, in an analysis step 33, the total product concentration α and/or the solids content β and/or the dissolved product content γ and/or the impurity content δ is determined from the electrical impedance, the measured temperature and the calibration matrix.

[0099] FIG. 10 shows another embodiment of the method according to the invention. Based on the determination of the total product concentration α and/or the solids content β and/or the dissolved product content γ and/or the impurity content δ described earlier, the control of the process is adjusted to increase efficiency.

[0100] Specifically, the crystalline solids content β is removed 34 when there is a sufficient degree of crystallization and a sufficient crystal size.

[0101] In addition, solvent is replenished 35 into the feed unit 2 or the solvent is partially replaced 36 when the impurity concentration exceeds a limit.

[0102] Furthermore, product is supplied 37 into the feed unit 2 so that the total product concentration α in the solution or suspension remains substantially constant during operation.