Method for operating a fractionator

Abstract

The present invention relates to a method for operating a rectification column 1000 for separating a mixture S containing a component A and a component B having a boiling point higher than that of component A, at an operating pressure of the rectification column 1000 below ambient pressure, the method comprising the steps of controlling a mass fraction P1 of component B in a product stream of component A to a value within a first target range of 0.1% to 5.0% and controlling a mass fraction P2 of component A in a product stream of component B to a value within a second target range of 0.1% to 5.0%, the control being in response to a control temperature TC, with respect to which a set point TC setpoint But T.C. setpoint = T2 + F (T1-T2), where F is a coefficient ranging from 0.1 to 0.9, T1 and T2 are the reference temperatures, and the set point TC setpoint If a deviation of the measured control temperature TC from the refrigeration column is found, the control temperature TC is determined by the following operating variables: (i) the heating of the column bottom 130 by the evaporator 200; (ii) the mass flow rate m of the reflux A42 fed back to the rectification column; A42 , (iii) the mass flow rate m of product stream P2 P2 and (iv) the mass flow rate m of product stream P1. P1 By varying one or more of the set points TC setpoint The present invention provides a method for adjusting the frequency of a signal to a predetermined frequency.

Description

[Technical field]

[0001] The present invention relates to a method for operating a rectification column 1000 for separating a mixture S containing a component A and a component B having a boiling point higher than that of component A, at an operating pressure of the rectification column 1000 below ambient pressure, the method comprising the steps of controlling a mass fraction P1 of component B in a product stream of component A to a value within a first target range of 0.1% to 5.0% and controlling a mass fraction P2 of component A in a product stream of component B to a value within a second target range of 0.1% to 5.0%, the control being in response to a control temperature (TC), with respect to the control temperature TC being controlled by a set point TC setpoint But T.C. setpoint =T2+F·(T1-T2), where F is a coefficient ranging from 0.1 to 0.9, preferably from 0.3 to 0.7, T1 and T2 are reference temperatures, and the set point TC setpoint If a deviation of the measured control temperature TC from the refrigeration column is found, the control temperature TC is determined by the following operating variables: (i) the heating of the column bottom 130 by the evaporator 200; (ii) the mass flow rate m of the reflux A42 fed back to the rectification column; A42 , (iii) the mass flow rate m of product stream P2 P2 and (iv) the mass flow rate m of product stream P1. P1 By varying one or more of the set points TC setpoint The present invention provides a method for adjusting the frequency of a signal to a predetermined frequency. [Background technology]

[0002] In many manufacturing processes, there is a separation operation, which separates a mixture of two or more components into its constituent components. As long as the thermal stability, volatility and boiling point differences of the components to be separated allow, such a separation operation is usually achieved by continuous rectification in industrial production. In the simplest case of a mixture S, consisting essentially of two components A and B, where B has a higher boiling point than A under the operating conditions selected for the rectification column used, the objective is to transfer B to the bottom of the column or to a side stream taken off at the bottom of the column and A to a side stream taken off at the top of the column or to a side stream taken off at the top of the column, so that one component contains as little as possible of the other component. Depending on the structure and operating conditions of the rectification column used, the concentration of A at the outlet point of A and the concentration of B at the outlet point of B vary (concentration profile).

[0003] The present invention relates to such a separation task, i.e. the separation of a mixture S consisting essentially (apart from impurities) only of the two components A and B. Rectification columns suitable for such separation tasks (as well as more demanding separation tasks) are in principle known from the prior art. The present invention relates to the specific concept of controlling such a rectification column, in particular using temperature control to control the position of the concentration profile.

[0004] Control of the position of the concentration profile of a rectification column by directly using the column temperature as a control variable is known per se and is widely used. For this purpose, a position in the column temperature profile is sought that reacts very sensitively to disturbances. This position is typically determined using simulation studies for various operating conditions. The column temperature at the position thus determined is then used as the control temperature.

[0005] However, if pressure fluctuations occur in the column at the location where the control temperature is measured, they will affect the boiling point and therefore the control temperature. This will lead to undesirable reactions of the controller and ultimately to impaired control quality. Such pressure fluctuations can be caused primarily by pressure fluctuations at the top of the column. However, they can also occur even with a constant pressure at the top as a result of increased or decreased pressure losses in the column due to changes in the column load. If pressure effects dominate composition effects, the desired control quality can only be achieved over a small pressure and load range.

[0006] For this reason, in many cases, instead of the measured column temperature as the control variable, a pressure-compensated temperature calculated from the measured column temperature is used. The usual procedure here is to determine the pressure dependence of the boiling point at the temperature sensor's location by column simulation calculations, to fit an equation, e.g. the known Antoine equation, to the data, to calculate a pressure-compensated temperature from there and to use it as control variable to control the column. The disadvantage of this method is that additional pressure sensors are required. These are also more susceptible to malfunctions and less accurate than temperature sensors. Pressure measurements frequently show an increasing time-dependent deviation (drift), resulting for example from hydraulic fluid losses or process-related fouling or deposits.

[0007] In the case of packed columns, further problems exist: the control temperature is usually measured in the packed bed. The pressure cannot be reliably measured in the packed bed because of the liquid flow. Instead, the pressure measuring device is installed in the area of ​​the pure gas phase, for example under the liquid collector or above the liquid distributor. In this case, the pressure at the location of the temperature measuring device is shifted by the pressure difference through such internals relative to this pressure measuring device. This pressure difference is also not constant but depends on the hydrodynamic properties of the column, which in turn depends on the throughput. To solve this problem, it is in principle conceivable to provide pressure measuring devices above and below the temperature sensor for the control temperature, respectively, but this further reduces the reliability of the device. Such problems can become so great that temperature control under certain conditions causes more problems than it solves (see non-patent document 1).

[0008] To use this approach, it is also necessary that deviations resulting from measurement errors in the temperature and pressure measurements only have a small effect on the calculated pressure-compensated temperature. However, especially for chemicals with small boiling point differences, the achievable accuracy of the pressure measurement is often not sufficient, so that pressure compensation of the controlled temperature does not lead to the desired control quality.

[0009] To overcome the above problems, control systems based on temperature difference measurements have been developed. In this case, a reference temperature measurement is inserted at a location in the column whose boiling point is only slightly dependent on the composition. The temperature difference between this reference temperature measurement and the control temperature measurement is used to control the column. In this way, pressure changes in the column can be compensated to a certain extent, but pressure difference changes, which also depend on the column load, cannot be compensated.

[0010] Kister, in "Temperature Sensing and Temperature Compensation," Vol. 2, No. 1, pp. 1111-1115, 2003, describes an approach by Boyd that uses two temperature differentials, i.e., four temperature sensors in total, to compensate for the effects of pressure differentials. The disadvantages of this procedure are: a) The temperatures used to form this difference are necessarily very close to each other, so the temperature measurements must be very accurate. b) The calculation of the control temperature difference is very complex and, in case of malfunction, is no longer understandable to the plant operator. c) Four temperature sensors are required. d) This method, according to Boyd, can only be used if the maximum permitted content of impurities in the product is in the ppm range and not in the percentage range (ibid., p. 557). e) Furthermore, Kister demonstrates (ibid., p. 563) that the control is not stable for large disturbances. On the contrary, a "runaway" may occur, in which the direction of action of the control circuit is reversed and the controller, instead of reducing the deviation, increases it, causing the process to move further away from the intended state. The reason for this is that the measured temperature difference has a maximum value as a function of the product quality, and its slope reverses after passing through the maximum value. Thus, for disturbances above a certain magnitude, the process becomes unstable.

[0011] US Patent No. 5,399,633 discloses a method and apparatus for controlling temperature in a fractionation column. This patent is directed to fractionation involving the separation of components with widely different boiling points. In this case, a zone of abrupt composition change from one tray to the next exists in the column. Above and below this zone of abrupt composition change are zones of relatively gradual concentration change. Application of heat or reflux to the column drives these zones up and down in the column, which creates problems such as sluggish or over-responsive control. To overcome this problem, this patent teaches placing multiple temperature sensing probes in the separation column at specific spaced locations throughout the column to obtain temperature measurements related to the composition behavior of the column, thereby automatically controlling the operation of the column in response to calculations of the multiple temperature measurements. More specifically, the computer adds the signals received from the middle of the column and the top and bottom of the column separately, subtracts the composite signal of the upper and lower zone probes from the composite signal of the middle probe, divides the resulting difference by the difference between the number of probes located in the middle of the column and the number of probes located at the top and bottom of the column, which is greater than one, and sends a signal to a controller, which sends a signal to a control valve that controls, for example, the volume of heated fluid entering the column through a control valve. Because this invention relies on maintaining a specific absolute temperature between the three middle temperature probes and the sum of the top and bottom temperatures, it cannot be used to separate components with closely differing boiling points. In the event of a change in pressure drop, for example due to a change in vapor flow, the profile in the column will shift.

[0012] US Pat. No. 5,399,633 discloses a fractionation heat balance control system. The invention is specifically directed to maintaining a fractionation column in heat equilibrium consistent with the characteristics of the feed stream. In particular, the objective of US Pat. No. 5,399,633 is to provide a control system that maintains heat equilibrium and simultaneously enhances separation efficiency. These objectives are stated to be accomplished by sensing six temperatures at selected points throughout the fractionation column. The six temperatures are separated into three specific pairs, each of which is used to measure the temperature difference ΔT between the two points. The first pair of temperature sensing means is vertically spaced below the feed location (or feed tray) and both are proximate to the feed location. A signal representative of ΔT between these points is utilized to regulate the enthalpy of the reboiler bottom liquid portion that is partially vaporized and returned to the reboiler section. The second pair of temperature sensors is vertically spaced below the feed introduction location, with one sensor proximate to the feed location and the other proximate to the location where the partially vaporized liquid bottom material is returned to the reboiler section of the column. The signal representative of ΔT between these two remote points is transmitted to a ΔT calculation (summing) means. A third pair of temperature sensors are spaced vertically above the feed location, one adjacent the feed location and the other adjacent the location where the reflux is returned to the rectifying section of the column. Another signal representative of the ΔT between these two remote points is also sent to a ΔT summing means. The summing means generates yet another signal representative of the difference between these two ΔT, and this last signal is used to regulate the amount of reflux to the column. The drawbacks of this method, particularly the control instability above a certain threshold resulting in a "runaway" concentration, are discussed in detail in Kister, J. Appl. Phys. 1999, 143:1311-1323 (see above).

[0013] There is therefore a need for further improvements in the field of separating mixtures into components, in particular where the quality of the individual components is maintained even under changed boundary conditions such as pressure fluctuations and changes in the hydraulic load of the equipment used, for example as a result of changes in the size of the feed stream. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] U.S. Patent No. 3,830,698 [Patent Document 2] U.S. Patent No. 4,024,027 [Non-patent literature]

[0015] [Non-Patent Document 1] Luyben, Practical Distillation Control, 1992, Van Nostrand Reinhold, p. 158 [Non-Patent Document 2] Distillation Operation, 1990, McGraw-Hill Education, pp. 555 to 557 and pp. 563 to 566 Summary of the Invention

[0016] In consideration of this requirement, the present invention provides the following:

[0017] A method for separating a mixture S containing a component A and a component B having a boiling point higher than that of component A, comprising operating a fractionator 1000 at an operating pressure of the fractionator 1000 that is less than ambient pressure, comprising the steps of: the sum of the mass fractions of components A and B in the mixture S is at least 95.0% relative to its total mass, from which a first product stream P1 comprising component A and a second product stream P2 comprising component B (and optionally further streams, in particular a low boiler-containing stream A21 (see also Figures 2, 3 and 4) and a high boiler-containing stream B11 (see also Figures 3 and 4)) are obtained, The fractionator 1000 comprises (at least) the following devices: (I) a vertical column body 100 including a stripping section 110 having separation internals and a rectification section 120 disposed thereon and having separation internals; (II) a column bottom 130 below the stripping section, containing a liquid bottom fraction B1, wherein a first temperature measuring device TM1 for measuring a first reference temperature T1 is arranged in the stripping section 110 or in the column bottom 130; (III) a top 140 above the rectification section, which contains the gaseous overhead fraction A1; (IV) A supply point 150 for the mixture S, disposed between the stripping section 110 and the rectification section 120, the mixture S being fed at a mass flow rate m S to the rectification column 1000 at a feed point 150; (V) an evaporator 200 for heating the column bottom 130 (e.g., by indirect heating of a portion B12 of the bottom fraction B1 with a heat transfer medium W, in particular steam); (VI) a second product stream P2 at a mass flow rate m P2 a bottom or side outlet unit 220 discharging at (VII) a condenser 300 (located inside or outside the rectification column 1000) for partially condensing the gaseous overhead fraction A1 to obtain a liquid overhead fraction A2 and a fraction composed of non-condensable components A3 (including low boilers and any gases (e.g. inert gases) that may be present that are not condensable under normal industrial conditions (minimum condensation temperature 20° C.), (VIII) distilling the first product stream P1 as a first portion of the distillation fraction A4 at a mass flow rate m P1 a top or side outlet unit 310 for removing a second portion of the distillation fraction A4 at a reflux ratio r=m A42 / m P1 The reflux A42 is provided with a mass flow rate m so that the reflux A42 moves through at least a portion of the rectification section 120 such that A42 (distillation fraction A4 may comprise the liquid overhead fraction A2 or its components or may be identical to the liquid overhead fraction A2), (IX) a second temperature measuring device TM2 arranged in the rectification section 120 or the top section 140, for measuring a second reference temperature T2; (XI) a third temperature measuring device TM3 for measuring a control temperature TC, which is arranged in the tower body 100 between the first temperature measuring device TM1 and the second temperature measuring device TM2; Equipped with The method includes adjusting the mass fraction of component B in the first product stream P1 (hereinafter also referred to as ω(B,P1)) to a first intended value (hereinafter ω(B,P1)) within a first target range of 0.1% to 5.0% relative to the total mass of the first product stream P1. INT and controlling the mass fraction of component A in the second product stream P2 (hereinafter also referred to as ω(A,P2)) to a second intended value (hereinafter also referred to as ω(A,P2)) within a second target range of 0.1% to 5.0% relative to the total mass of the second product stream P2. INT The control is performed in response to a control temperature TC, and a set point TC setpoint is calculated according to the following formula: T.C. setpoint =T2+F·(T1-T2) (I) In the formula, F is a coefficient in the range of 0.1 to 0.9, preferably in the range of 0.3 to 0.7. The first reference temperature T1, the second reference temperature T2, and the control temperature TC are measured continuously or at intervals, and the set point TC of the measured control temperature TC is set. setpoint If a deviation from is found, the control temperature TC is adjusted based on the following operating variables: (i) Heating of the column bottom 130 by the evaporator 200, (ii) Mass flow rate m of reflux A42 fed back to the rectification column A42 , (iii) the mass flow rate m of the second product stream P2 P2 and (iv) the mass flow rate m of the first product stream (P1). P1 By varying one or more of the set points TC setpoint will be readjusted to.

[0018] The coefficient F is a predetermined coefficient, i.e., the coefficient F is determined before actual control of the mass fractions of B in P1 (i.e., ω(B,P1)) and A in P2 (i.e., ω(A,P2)) occurs as part of the operation of the rectification column. In particular, F is calculated based on the temperatures of TM1, TM2 and TM3, respectively, at the intended operating conditions of the column (i.e., the intended conditions with respect to the mass fractions of component B in the first product stream P1 and component A in the second product stream P2, the respective temperatures being designated hereinafter with the subscript "INT"), according to the following formula (II): F=(TC INT -T2 INT ) / (T1 INT -T2 INT ) (II)

[0019] T1 INT , T2 INT and T.C. INT can be determined by a computer simulation of the rectification column and / or by one or more measurements obtained during testing with the rectification column itself or a suitable representation thereof, such as a pilot plant or laboratory column.

[0020] In the case of computer simulations, of course, there are no real (physical) temperature measuring devices TM in the computer models used, and in such cases the expressions "temperature at TM1 / TM2 / TM3" refer to the temperatures at positions in the fractionation column suitable for installing the respective temperature measuring devices in real operation.

[0021] For TM1 this is a location in the stripping section or bottom of the column, for TM2 a location in the rectifying section or top of the column, for TM3 this is a location in the body of the column between TM1 and TM2, a location that is particularly suitable for TM3 being the location of maximum dependence of the temperature profile on changes in operating conditions, as will be explained in more detail below.

[0022] The ratio F calculated using equation (II) is essentially constant under changing pressure conditions. Therefore, once F is determined, it can be calculated using equation (I) to determine the set point TC of the control temperature TC during operation of the column. setpoint can be used to calculate the mass fraction of component B in the first product stream P1 and the mass fraction of component A in the second product stream P2. Control of the mass fraction of component B in the first product stream P1 and the mass fraction of component A in the second product stream P2 is then performed as described above. In other words, the present invention provides a method for operating a rectification column 1000, which in particular separates a mixture S containing a component A and a component B having a boiling point higher than that of component A, at an operating pressure of the rectification column 1000 below ambient pressure as described above, where the coefficient F is calculated according to formula (II) where T1 INT , T2 INT and T.C. INT are the temperatures at TM1, TM2 and TM3, respectively, at the intended state of operation of the rectification column, and the intended state is ω(B,P1)=ω(B,P1) INT and ω(A,P2)=ω(A,P2) INT It is.

[0023] For the purposes of the present invention, a rectification column, as known to those skilled in the art, is a process unit for the thermal separation of mixtures, which operates according to the principle of rectification, i.e. in which vapors are contacted in countercurrent with a liquid many times in succession. Examples of rectification columns include packed columns or tray columns. The contact area between the vapor and liquid phases is provided by separation internals constituting the stripping and rectification sections.

[0024] The term "separation internals" in the present terminology refers to equipment inside the column body that enhances contact and mass transfer between the vapor and liquid phases so that more volatile components tend to migrate to the vapor phase and less volatile components tend to migrate to the liquid phase, thereby providing a separation effect according to the boiling point difference. The separation internals can in particular be one or more trays or one or more packed beds using structured or random packing.

[0025] The term recovery section (110), in the terminology of the present invention, refers to the area below the feed point 150 of the mixture S to be separated, and includes the totality of all separation internals present in this area.

[0026] The term rectification section (120) in the present terminology refers to the region above the feed point 150 and includes the totality of all separation internals in this region. The term "separation internals" is conventional in the field and does not necessarily mean that the stripping section and the rectification section each have to contain a plurality of internals. The present invention encompasses embodiments in which the stripping section and the rectification section are each formed, for example, by one packed bed (also shown in FIG. 1). The structure of such separation internals (whether in the stripping section or in the rectification section) is known to those skilled in the art and therefore does not require further explanation at this point. Instead of rectification column, the term column is also used below for short. The two terms are used synonymously in the present terminology.

[0027] Components A and B can be pure substances or mixtures, in particular mixtures of isomers. An example of the latter case can be toluenediamine (TDA), without the invention being limited thereto. TDA exists in various isomers, which may be called ortho-TDA, meta-TDA and para-TDA, depending on the position of the two amino groups relative to each other. In each case, various isomers of meta-TDA and ortho-TDA are present, namely 2,4-TDA, 2,6-TDA and 3,5-TDA for the former and 2,3-TDA and 3,4-TDA for the latter. In the industrial production of TDA by hydrogenation of dinitrotoluene (DNT) obtained by dinitration of toluene, only the ortho- and meta-isomers play a role, and in the case of meta-TDA, only 2,4-TDA and 2,6-TDA are relevant. 2,5-TDA (para position of the amino group) and 3,5-TDA (meta position of the amino group) are produced in negligible amounts, if at all. During the process of purification by rectification of the crude TDA obtained from the hydrogenation, ortho-TDA and meta-TDA are separated from each other without separation of the individual isomers, since the boiling point difference between the two related meta isomers on the one hand and the two ortho isomers on the other hand is very small compared to the boiling point difference between the lowest boiling meta-TDA isomer and the highest boiling ortho-TDA isomer. In the terms of the present invention, ortho-TDA can be considered as a whole as component A and meta-TDA can be considered as a whole as component B, i.e. in this case component A is a mixture of 2,3-TDA and 3,4-TDA, and component B is a mixture of 2,4-TDA and 2,6-TDA.

[0028] The requirement according to the present invention that component B has a higher boiling point than component A should be interpreted to mean that, when one or both components comprise multiple components, the highest boiling component of component A boils at a lower temperature than the lowest boiling component of component B.

[0029] The term low boilers refers to organic secondary components whose boiling point is lower than that of component A or the lowest boiling component of component A. The term high boilers refers to organic secondary components whose boiling point is higher than that of component B or the highest boiling component of component B.

[0030] The relative volatility α of two components A and B is a measure of their thermal separability and is expressed as follows: α = (y A x B ) / (y B x A ) where y is the mole fraction of the component in the vapor and x is the mole fraction of the component in the liquid in thermodynamic equilibrium with the vapor phase. When A and B consist of multiple materials, in particular isomers only, y and x are cumulative parameters, respectively. An example would be where component B is meta-TDA, i.e. a mixture of 2,4-TDA and 2,6-TDA (the presence of traces of 3,5-TDA can be ignored for the purposes of the present invention and does not depart from the scope of the invention), and component A is ortho-TDA, i.e. a mixture of 2,3-TDA and 3,4-TDA. The mole fraction of meta-TDA x B , x meta-TDA is in this case the sum of the mole fractions of the individual components 2,4-TDA and 2,6-TDA. The molar amount of 2,4-TDA or 2,6-TDA in the liquid, respectively, n 2,4-TDA(L) or n 2,6-TDA(L) The total amount of moles in the liquid is expressed as n (L) Then, the following formula applies: x B =x meta-TDA =[n 2,4-TDA(L) / n (L) ]+[n 2,6-TDA(L) / n (L) ] The corresponding equation is x A , y A , and y B applies to.

[0031] The mixture S, the separation of which is the focus of the present invention, can contain, in addition to components A and B, up to 5.0% by weight of impurities. If no further streams other than product streams P1 and P2 are taken off from rectification column 1000, such impurities, depending on their boiling point, either enter product stream P1 together with component A (if they are less volatile impurities discharged by stream A3) or enter product stream P2 together with component B. If necessary, such impurities can be removed from product streams P1 and P2 in further distillation steps.

[0032] The first intended value ω(B,P1) INT and the second intended value ω(A,P2) INT can refer to specific values ​​of mass fractions within the first and second target ranges, respectively, e.g., 1.0%, (which specific values, of course, include any inherent tolerances). Similarly, they can refer to tolerance ranges within the first and second target ranges, respectively, e.g., (1.0±0.5)%, i.e., 0.5% to 1.5%, respectively.

[0033] All pressures reported are absolute pressures. In the terminology of the present invention, the expression "operating pressure of the rectification column" means the pressure at the top of the column.

[0034] Surprisingly, it has been found that the above-mentioned problem in the field of separating mixtures into components, of the unaltered quality of the individual components, can be solved or at least alleviated if the fractionation column used to separate the mixture is operated according to the method of the invention. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 shows a possible embodiment of a fractionator 1000 that can be operated according to the process of the present invention, in which a first product stream P1 is taken from the top and a second product stream P2 is taken from the bottom. [Diagram 2]1 shows a possible embodiment of a rectification column 1000 that can be operated according to the process of the present invention, in which a first product stream P1 is taken as a side stream and a second product stream P2 is taken as a bottom stream. In the embodiment shown, the rectification section 120 consists of two packed beds 121 and 122. [Diagram 3] FIG. 1 shows a further possible embodiment of a rectification column 1000 that can be operated according to the process of the present invention, in which a first product stream P1 and a second product stream P2 are removed as side streams. [Figure 4] FIG. 1 is a reproduction of the dividing wall column shown in FIG. 1 of EP 1 746 083 (applying the device and stream terminology used herein), with indications of suitable locations of temperature measuring devices TM1, TM2 and TM3 when the column is operated using the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] First, a brief overview of various possible embodiments of the invention is provided below.

[0037] In a first embodiment of the present invention which can be combined with all other embodiments, component A and component B have a relative volatility α in the range of 1.05-10.

[0038] In a second embodiment of the present invention, which is a specific configuration of the first embodiment, the relative volatility α is within the range of 1.3 to 3.

[0039] In a third embodiment of the invention, which can be combined with all other embodiments, the first temperature measuring device TM1 is arranged at the bottom of the column.

[0040] In a fourth embodiment of the invention, which can be combined with all other embodiments, the second temperature measuring device TM2 is arranged in the rectification section.

[0041] In a fifth embodiment of the invention, which can be combined with all other embodiments, the third temperature measuring device TM3 is arranged at a position in the tower body 100 where component A is present in a mass fraction ranging from 30% to 70% relative to the total mass of A and B (and component B is consequently present in a mass fraction ranging from 70% to 30% relative to the total mass of A and B).

[0042] In a sixth embodiment of the present invention, which can be combined with all other embodiments, the coefficient F is in the range of 0.3 to 0.7.

[0043] In a seventh embodiment of the invention, which can be combined with all other embodiments, the operating pressure (at the top of the column 140) is equal to or greater than a value p B and the value p B varies by no more than ±35% during operation of fractionator 1000.

[0044] In an eighth embodiment of the present invention, which can be combined with all other embodiments, to determine the coefficient F: (A) The first intended value (ω(B,P1) INT ) and the second intended value (ω(A,P2) INT ), (B) The first intended value (ω(B,P1) INT ) and the second intended value (ω(A,P2) INT Establishing the requirements that the rectification column 1000 must meet, taking into account the above factors, including the number of theoretical stages, the location of the feed point 150, and the operating pressure; (C) determining the temperature profile of the rectification column from the requirements established in (B) by computer-aided simulation and / or measurements (especially in a laboratory plant); (D) determining the dependence of the temperature profile on changes in operating conditions and establishing the position within the temperature profile where this dependence is maximum, the operating conditions being: Heating of the column bottom 130 by the evaporator 200, the reflux ratio r, the mass flow rate m of the first product stream P1 P1, the mass flow rate m of the second product stream P2 P2 , the composition of the feed and the mass flow rate of the feed m S , and (E) establishing the position of the first temperature measuring device TM1 at the bottom 130 or stripping section 110, the position of the second temperature measuring device TM2 at the top 140 or rectification section 120, and the position of the third temperature measuring device TM3 at the positions of maximum dependence of the temperature profile on the changes in the operating conditions determined in (D), where such deviations from this "ideal" or "theoretical" position of maximum dependence due to practical operating constraints, in particular due to the spatial boundary conditions of the rectification column, do not depart from the scope of this embodiment; (F) determining the coefficient F under the boundary conditions established in (A) to (E) by computer-aided simulation and / or measurements (in the fractionator under consideration or in an experimental plant); is executed, The set point TC of the control temperature TC is set using the coefficient F determined in (F). setpoint To determine (G) inputting a factor F into a process control system that controls the distillation column 1000; (H) A set point TC of the control temperature TC is calculated from a first reference temperature T1 measured during the operation of the distillation column 1000 and a second reference temperature T2 measured during the operation of the distillation column 1000. setpoint and calculating is executed.

[0045] In a ninth embodiment of the invention, which can be combined with all other embodiments, component A comprises a mixture of 2,3-toluenediamine and 3,4-toluenediamine and component B comprises a mixture of 2,4-toluenediamine and 2,6-toluenediamine.

[0046] In a tenth embodiment of the present invention, which is a specific configuration of the ninth embodiment, the tower bottom 130 is heated by an evaporator 200 to a temperature in the range of 150°C to 250°C.

[0047] In an eleventh embodiment of the present invention, which is a specific configuration of the ninth embodiment, the reflux ratio r is within the range of 20-100.

[0048] In a twelfth embodiment of the present invention, which is a specific configuration of the ninth embodiment, a value p in the range of 50 mbar to 250 mbar is used. B is set for the operating pressure (measured at the top of the column 140).

[0049] In a thirteenth embodiment of the present invention, the rectification column 1000 is a packed column. This embodiment can be combined with all other embodiments, as long as it does not exclude that the rectification column 1000 is configured as a packed column.

[0050] In a fourteenth embodiment of the present invention, the fractionator 1000 is a tray column. This embodiment can be combined with all other embodiments, as long as they do not exclude the fractionator 1000 being configured as a tray column.

[0051] In a fifteenth embodiment of the invention, which can be combined with all other embodiments, the coefficient F is calculated according to formula (II). F=(TC INT -T2 INT ) / (T1 INT -T2 INT ) (II) In the formula, T1 INT , T2 INT and T.C. INT are the temperatures at TM1, TM2 and TM3, respectively, at the intended state of operation of the rectification column, and the intended state is ω(B,P1)=ω(B,P1) INT and ω(A,P2)=ω(A,P2) INT It is.

[0052] The above-mentioned embodiments and further possible variants of the invention are described in more detail below. All embodiments and further implementation options can be combined with each other in any way, unless the context clearly indicates to the contrary to the skilled person or unless something different is explicitly stated.

[0053] Since temperature measurements have a significantly higher accuracy than pressure measurements, only temperature measurements are used in the method according to the invention to carry out the control tasks. Moreover, the measured boiling point is a function of pressure for a fixed composition, in particular for a pure material. Therefore, the temperatures at the top (or rectifying section) and bottom (or stripping section) of the column can be used as an indication of the pressure there.

[0054] In the following, columns are described that are operating at various pressures, but in the intended state with respect to the product quality being controlled. An increase in pressure at the top results in a corresponding increase in pressure throughout the column. This gives an equivalent temperature increase at both the bottom and the top, and at the location where the control temperature is measured. Thus, the relative (TC-T2) / (T1-T2) remains approximately constant.

[0055] Then, if the pressure difference across the column increases, the pressure at the top (or rectifying section) and therefore also the temperature remain constant, but the pressure and temperature at the point where the control temperature is measured and at the bottom (or stripping section) increase. Here, the increase in pressure and temperature is greatest at the bottom, since the pressure difference across the column is decisive for this, while only the pressure difference between the measurement point and the top is decisive for the pressure and temperature at the point where the control temperature is measured.

[0056] The present invention relates in particular to a process for producing a mixture of components A and B which has a relative volatility α in the range of 1.05 to 10, particularly preferably in the range of 1.3 to 3. (TC-T2) / (T1-T2) remains approximately constant with changes in pressure, so long as the pressure change is not too large (in particular, not more than 35%, preferably not more than 30%, of the original pressure, ie, the pressure before the pressure change occurs).

[0057] It follows from this that if the column is operating correctly with respect to the controlled product quality, the ratio (TC-T2) / (T1-T2) will remain approximately constant even when the overhead pressure or pressure differential in the column changes.

[0058] This fact is exploited by a newly developed control concept: the ratio (TC-T2) / (T1-T2) is calculated based on the temperature at the intended state of the column (i.e., (TC INT -T2 INT ) / (T1 INT -T2 INT ) is calculated) and stored as a constant coefficient F (equation (II)). The temperature TC obtained at the measurement location under intended conditions CALC can be calculated during tower operation using the following formula: T.C. CALC =T2+F·(T1-T2)

[0059] where F is the coefficient (predetermined based on the temperature at the intended state of the column using formula (II), see above) and T1 and T2 are the measured (i.e., measured during operation) temperatures. The temperature TC thus calculated is CALC Then, the control temperature set point TC setpoint It is used as TC setpoint =TC CALC which results in formula (I).

[0060] A P (proportional) controller, a PI (proportional integral) controller, a PID (proportional integral derivative) controller, or another equivalent building block of control, preferably a PI controller, is usually used for the control. The controller output preferably influences one of: (i) the supplied evaporator duty, (ii) the reflux flow rate directly or indirectly, or (iii) the product stream P2 directly or indirectly, or (iv) the product stream P1 directly or indirectly. In the case of a direct influence, the controller output can directly control the setting of a valve, while in the case of an indirect influence, the normal output serves, for example, as the set point of a flow controller, which controller output then controls the setting of the valve.

[0061] A rectification column 1000 which can be operated using the method of the invention is shown by way of example in FIG. 1 (the accompanying drawing shows a rectification column suitable for use with the method of the invention as an example of a packed column; other types of rectification column, e.g. tray columns, are of course equally suitable).

[0062] The mixture S to be separated is fed to the column 1000 in the central region via the feed point 150 at a mass flow rate m S to the rectification column 1000. The stripping section 110 and the rectification section 120 each consist of a packed bed in the selected example, which should be construed as merely illustrative and does not constitute any limitation.

[0063] The column bottom 130 is provided with a part of the bottom fraction B1 (mass flow rate m B12 The second product stream P2 is in this embodiment a further part (=B11) of the bottom fraction B1 and is heated indirectly by the heat transfer medium W, in particular by steam, by recycling the bottom fraction B12 (=B11) to the column 1000 via the evaporator 200. The amount of heat transfer medium W introduced and therefore the heating duty can be set via the heat transfer medium valve 210. The second product stream P2 is in this embodiment a further part (=B11) of the bottom fraction B1 and is heated indirectly by the heat transfer medium W, in particular by steam, by recycling the bottom fraction B12 (=B11) to the column 1000 via the evaporator 200. P2 (In this embodiment, m B11The mass flow rate m B12 and m B11 The ratio is set by the bottom circuit valve 230.

[0064] At the top of the column 140, the vaporized overhead fraction A1 is taken off and partially liquefied in a condenser 300 arranged outside the column body 100. It is not necessary to arrange the condenser 300 outside the column body 100 (see also figures 2 and 3). Non-condensable components A3 are taken off in gaseous form. These non-condensable components A3 comprise impurities having a boiling point lower than that of the second product stream P2 (so-called low boilers) and any gases present that are not condensable under normal industrial conditions (minimum condensation temperature 20°C) (for example inert gases). The condensed components A2, which in this embodiment are identical to the distillation fraction A4, are returned to the column 1000 by the reflux splitter 320 at a mass flow rate m A42 and the first product stream (i.e. P1=A41) with a mass flow rate m P1 (=m A41 ) and stream A41, which is taken off at 100° C. In the embodiment of FIG. 1, the first product stream P1 thus has the same composition as the liquid overhead fraction A2. The ratio of the mass flows m A42 / m P1 is referred to as the reflux ratio r. Suitable (non-limiting) locations for temperature measuring devices TM1, TM2, and TM3 are shown.

[0065] FIG. 2 shows a further possible configuration of a rectification column 1000 that can be operated using the method of the invention. The repeated reference numbers have the same meaning as in FIG. 1. In contrast to the column shown in FIG. 1, the condenser 300 here is located at the top of the column and the rectification section 120 is formed by two packed beds 121, 122 located above and below the side outlet of the distillation fraction A4. A second temperature measuring device TM2 can be arranged in each of the two packed beds 121, 122. The condensate obtained in the condenser 300 (= liquid overhead fraction A2) flows downwards inside the column body 100 in this embodiment through the upper part 122 of the rectification section 120. Below the packed bed 122 there is a liquid collector (not shown) in which the liquid A22 dripping from the upper packed bed 122 is collected and discharged from the column body 100 as the distillation fraction A4. The distillation fraction A4 is split into reflux A42 and the first product stream (P1=A41) as described for FIG. 1. Alternatively, only the first product stream P1 can be discharged from the column body 100, while the reflux stream is fed to the lower packed bed 121 in the column body. As shown in FIG. 2, a low boiler-containing stream A21 can be discharged from the liquid overhead fraction A2. Depending on how much and to what extent component A is still present in this low boiler stream, it may be useful to feed stream A21 to a further distillation in order to isolate A. However, the mass ratio of streams A21 to A22 is typically very small in such a case, in particular in the range of 0.001 to 0.05. Whether it is useful to take off low boilers A21 in this way depends on the particular separation task, in particular the low boiler content of the mixture S, and can be easily determined in a particular case by the person skilled in the art. Suitable (but not limiting) positions of the temperature measuring devices TM1, TM2 and TM3 are shown.

[0066] FIG. 3 shows a variant of the embodiment shown in FIG. 2, in which a second product stream P2 is obtained as a side stream immediately below the stripping section 110, while the discharged part B11 of the bottom stream B1 is used to take off the high boilers. In this embodiment, the second product stream P2 is therefore different from the stream B11. Depending on the amount of component B present in the stream B11 and its scale, it may be useful to feed the stream B11 to a further distillation in order to isolate B. The configuration shown in FIG. 3 may be particularly useful when the mixture S to be separated contains a relatively large amount of high boilers. In the case where a large amount of high boilers is present, but only a small amount of low boilers, the low boiler outlet A21 may also be omitted, as already mentioned above. Suitable (non-limiting) positions of the temperature measuring devices TM1, TM2 and TM3 are shown.

[0067] The implementation options of the rectification column 1000 shown in the figure should not be construed as exhaustive. For example, it is possible and within the scope of the present invention to subject the gaseous fraction composed of the non-condensable constituent A3 to post-condensation in order to obtain a liquid stream containing secondary components (known as low boilers) having a boiling point lower than that of component A.

[0068] Regardless of the exact configuration of the rectification column, the following embodiments are preferred.

[0069] The first temperature measuring device TM1 is preferably arranged in the bottom of the column, and the second temperature measuring device TM2 is preferably arranged in the rectification section.

[0070] As regards the positioning of the third temperature measuring device TM3, it is preferably arranged at a position in the tower body 100 where component A is present in a mass fraction ranging from 30% to 70% relative to the total mass of A and B (and component B is consequently present in a mass fraction ranging from 70% to 30% relative to the total mass of A and B).

[0071] According to the invention, the coefficient F is in the range of 0.1 to 0.9, preferably in the range of 0.3 to 0.7. To determine a particular value of the coefficient F, the following procedure is carried out: (A) The first intended value (ω(B,P1) INT ) and the second intended value (ω(A,P2) INT ) and (B) The first intended value (ω(B,P1) INT ) and the second intended value (ω(A,P2) INT Establishing the requirements that the rectification column 1000 must meet, taking into account the above factors, including the number of theoretical stages, the location of the feed point 150, and the operating pressure; (C) determining, by computer-aided simulation and / or measurement (especially in a laboratory plant), the temperature profile of the rectification column from the requirements established in (B); (D) determining the dependence of the temperature profile on changes in operating conditions and establishing the position within the temperature profile where this dependence is maximum, the operating conditions including: Heating of the column bottom 130 by the evaporator 200, the reflux ratio r, and the mass flow rate m of the product stream P1 P1 , the mass flow rate m of product stream P2 P2 , the composition of the feed and the mass flow rate of the feed m S , and (E) establishing the position of the first temperature measuring device TM1 in the bottom 130 or stripping section 110, the position of the second temperature measuring device TM2 in the top 140 or rectification section 120, and the position of the third temperature measuring device TM3 at the positions of maximum dependence of the temperature profile on the changes in the operating conditions determined in (D); (F) determining the coefficient F under the boundary conditions established in (A) to (E) by computer-aided simulation and / or measurements (in the fractionator under consideration or in an experimental plant); It is preferred to use The set point TC of the control temperature TC is set using the coefficient F determined in (F). setpointTo determine (G) inputting a factor F into a process control system that controls the distillation column 1000; (H) The set point TC of the control temperature (TC) is calculated from the temperatures T1 and T2 measured during the operation of the distillation column 1000. setpoint and calculating is executed.

[0072] It will be easily understood by those skilled in the art that in practical operation, when establishing the position of the third temperature measuring device TM3, certain deviations from the "ideal" or "theoretical" position of the maximum dependence of the temperature profile on the change in operating conditions may be unavoidable. In particular, the spatial boundary conditions of the rectification column may require certain deviations from the position of the maximum dependence as determined in (D). For example, the position of the maximum dependence as determined in (D) may be located in a position of the rectification column where the installation of a temperature measuring device is very cumbersome or even physically impossible. Deviations from the "ideal" or "theoretical" position of the maximum dependence of the temperature profile on the change in operating conditions due solely to such unavoidable constraints do not depart from the scope of this embodiment.

[0073] The process of the invention can be used, for example, in the work-up of toluenediamine (TDA), in particular in the process for separating meta and ortho isomers from one another. In this case, component A comprises a mixture of 2,3-TDA and 3,4-TDA, and component B comprises a mixture of 2,4-TDA and 2,6-TDA. Preferred operating parameters for this use are as follows: The temperature of the tower bottom 130 is set to a range of 150°C to 250°C by the evaporator 200. The reflux ratio r is set to a value in the range of 20-100. The operating pressure pB is set to a value in the range of 50 mbar to 250 mbar.

[0074] In this way, for example, the column designated "A" in US Pat. No. 6,359,177 can be operated according to the method of the present invention.

[0075] It is also conceivable to operate the dividing wall column described in European Patent 1746083 (EP'083) according to the process of the present invention. As an example, in the embodiment shown in FIG. 1 of EP'083, the crude TDA inlet "A" corresponds to the mixture S of the present invention, the "stream containing ortho-TDA" ("P2" in EP'083 terminology) corresponds to the product stream P1 of the present invention, and the "stream containing meta-TDA" ("P3" in EP'083 terminology) corresponds to the product stream P2 of the present invention. Furthermore, the "stream containing low boilers" ("P1" in EP'083 terminology) corresponds to the low boiler-containing stream A21 of the present invention (as obtained in the embodiment shown in FIG. 3 of the present invention), and the "stream containing high boilers and m-TDA" ("P4" in EP'083 terminology) corresponds to the high boiler-containing stream B11 of the present invention (as obtained in the embodiment shown in FIG. 3 of the present invention). FIG. 4 shows a reproduction of FIG. 1 of EP'083, applying the terminology of the present invention to the devices and streams. The dividing wall is shown as 400 and the separating internals of the stripping section are shown as 111, 112 and 113. For operating the dividing wall column according to the process of the present invention, suitable locations for temperature measuring devices TM1, TM2 and TM3 are as follows:

[0076] Temperature measuring device TM2 measuring T2 is positioned slightly below the top of the isolation internal structure 120, temperature measuring device TM1 measuring T1 is positioned inside and slightly above the bottom of the isolation internal structure 113, and temperature measuring device TM3 measuring TC is positioned inside the isolation segment 120 (the exact location can be determined as described above).

[0077] The invention will now be described in detail with reference to examples.

[0078] Working Example: General conditions (base case): The separation of the isomer mixture of feed S consisting of 8000 kg / h 2,4-TDA, 2000 kg / h 2,6-TDA, 200 kg / h 2,3-TDA and 300 kg / h 3,4-TDA was simulated using a process simulation program (VTPLAN, equivalent to ASPEN). A column with 20 theoretical plates was assumed, where feed S was introduced at theoretical plate 13. An evaporator was located at the bottom of the column and a condenser was present at the top. The overhead pressure was assumed to be 100 mbar and the bottom pressure 120 mbar. The condensation temperature was set to 150 °C. The mass fraction of 2,3-TDA and 3,4-TDA (ortho-TDA) in the product stream P2 was 1.0% (=ω(A,P2) INT ) and the mass fraction of 2,4-TDA and 2,6-TDA (meta-TDA) in product stream P1 is 1.0% (=ω(B,P1) INT The evaporator duty and reflux were varied so that the evaporator pressure was 1653 kW and the reflux flow rate m of 9468 kg / h. A42 In the simulation calculations, it was found that at theoretical plate 7, the concentrations of meta-TDA and ortho-TDA are almost equal and the gradient of the temperature profile is particularly steep. A temperature of 195.63 °C was found at theoretical plate 7, which will be used to control the temperature in the following. A T2 of 184.82 °C was found at theoretical plate 7. INT A temperature of 210.87°C was found at the top, and a T INT A temperature of 0.01 was found at the bottom.

[0079] Example 1 (Comparative): In the simulation as described in general conditions, the evaporator duty was fixed at a constant 1653 kW. The control temperature was fixed at 195.63° C. To simulate a pressure disturbance, the pressure in the column was increased by 30 mbar uniformly throughout the column. In the simulation, this resulted in an increase in the mass fraction of ortho-TDA in stream P2 to 3.0%, while stream P1 now contained only 0.12% meta-TDA.

[0080] Example 2 (according to the present invention): In the simulation as described in General Conditions, the evaporator duty was fixed as in the non-inventive embodiment and the pressure was increased by 30 mbar. The factor F is calculated as 0.415 from the base case simulation calculation. As a result of the pressure change, the calculated temperature T1 increased to 217.75°C and T2 increased to 192.49°C. The control temperature TC of 202.97°C CALC =TC setpoint was calculated using the factor F, which in the simulation was set to theoretical plate 7. The content of ortho-TDA in stream P2 was found to be 1.1% and the content of meta-TDA in stream P1 was found to be 1.1%, thus deviating from the intended value of 1.0%, respectively, only within the range of typical process variations.

Claims

1. A method for separating a mixture (S) containing a component A and a component B having a boiling point higher than that of said component A, comprising operating a rectification column (1000) at an operating pressure of said rectification column (1000) that is less than ambient pressure, comprising: the sum of the mass fractions of the component A and the component B in the mixture (S) is 95.0% to 100% based on the total mass thereof, and a first product stream (P1) containing the component A and a second product stream (P2) containing the component B are obtained from the mixture (S); Said rectification column (1000) comprises the following devices: (I) a vertical column body (100) including a stripping section (110) having separation internals and a rectification section (120) disposed thereon and having separation internals; (II) a column bottom (130) below the stripping section, containing a liquid bottom fraction (B1), wherein a first temperature measuring device (TM1) measuring a first reference temperature (T1) is located in the stripping section (110) or in the column bottom (130); (III) a column top (140) above the rectification section, which contains a gaseous overhead fraction (A1); (IV) A feed point (150) for the mixture (S) arranged between the stripping section (110) and the rectification section (120), wherein the mixture (S) is fed at a mass flow rate m Ｓ a feed point (150) at which the rectification column (1000) is fed with (V) an evaporator (200) for heating the tower bottom (130); (VI) feeding the second product stream (P2) at a mass flow rate m Ｐ２ a bottom or side outlet unit (220) discharging at (VII) a condenser (300) (located inside or outside the rectification column (1000)) for partially condensing the gaseous overhead fraction (A1) to obtain a liquid overhead fraction (A2) and a fraction composed of non-condensable components (A3); (VIII) distilling the first product stream (P1) into a first portion of the distillation fraction (A4) at a mass flow rate m Ｐ１ a top or side outlet unit (310) for removing a second portion of said distillation fraction (A4) at a reflux ratio r=m Ａ４２ / m Ｐ１ The reflux (A42) is passed through at least a portion of the rectification section (120) so that a mass flow rate m Ａ４２ a top or side exit unit (310) conveyed by (IX) a second temperature measuring device (TM2) disposed in the rectification section (120) or the top of the column (140) and measuring a second reference temperature (T2); (X) a third temperature measuring device (TM3) for measuring a control temperature (TC) disposed in the tower body (100) between the first temperature measuring device (TM1) and the second temperature measuring device (TM2); Equipped with The method comprises the steps of controlling the mass fraction of the component B in the first product stream (P1) to a first intended value within a first target range of 0.1% to 5.0% relative to the total mass of the first product stream (P1) and controlling the mass fraction of the component A in the second product stream (P2) to a second intended value within a second target range of 0.1% to 5.0% relative to the total mass of the second product stream (P2), the control being responsive to the control temperature (TC), and relative to the control temperature (TC) being a set point TC ｓｅｔｐｏｉｎｔ is calculated according to the following formula: TC ｓｅｔｐｏｉｎｔ =T2+F・(T1-T2) F is a coefficient ranging from 0.1 to 0.9; The first reference temperature (T1), the second reference temperature (T2), and the control temperature (TC) are measured continuously or at intervals, and the measured control temperature (TC) is adjusted to its set point TC. ｓｅｔｐｏｉｎｔ If the temperature deviates from the reference temperature, the control temperature (TC) is adjusted based on the following operating variables: (i) the heating of the column bottom (130) by the evaporator (200), (ii) the mass flow rate m of the reflux (A42) fed back to the rectification column Ａ４２ , (iii) the mass flow rate m of the second product stream (P2) Ｐ２ and (iv) the mass flow rate m of the first product stream (P1). Ｐ１ by adjusting one or more of the set points TC ｓｅｔｐｏｉｎｔ The method is readjusted to

2. 2. The method of claim 1, wherein component A and component B have a relative volatility α in the range of 1.05 to 10.

3. 3. The method according to claim 1 or 2, wherein the first temperature measuring device (TM1) is arranged at the bottom of the column.

4. 3. The method according to claim 1 or 2, wherein the second temperature measuring device (TM2) is arranged in the rectification section.

5. 3. The method according to claim 1 or 2, wherein the third temperature measuring device (TM3) is arranged at a position in the column body (100) where the component A is present in a mass fraction ranging from 30% to 70% relative to the total mass of A and B.

6. The operating pressure has a value p Ｂ and said value p Ｂ 3. The method of claim 1, wherein the saturation temperature varies by no more than ±35% during operation of the rectification column (1000).

7. To determine the coefficient F, (A) specifying the first intended value and the second intended value; (B) establishing requirements that the rectification column (1000) must meet, taking into account the first intended value and the second intended value, said requirements including the number of theoretical stages, the location of the feed point (150), and the operating pressure; (C) determining, by computer-aided simulation and / or measurement, a temperature profile for the rectification column from the requirements established in (B); (D) determining the dependence of the temperature profile on changes in operating conditions and establishing the position within the temperature profile where this dependence is greatest, the operating conditions being: The heating of the column bottom (130) by the evaporator (200), the reflux ratio r, the mass flow rate (m Ｐ１ ), the mass flow rate (m Ｐ２ ), the composition of the feed and the mass flow rate of the feed (m Ｓ ), and (E) establishing the position of the first temperature measuring device (TM1) in the column bottom (130) or in the stripping section (110), the position of the second temperature measuring device (TM2) in the column top (140) or in the rectification section (120), and the position of the third temperature measuring device (TM3) at the positions of maximum dependence of the temperature profile on changes in operating conditions determined in (D); (F) determining the coefficient F under the boundary conditions established in (A) through (E) by computer-aided simulation and / or measurement; is executed, The set point TC of the control temperature TC is determined using the coefficient F determined in (F). ｓｅｔｐｏｉｎｔ To determine (G) inputting the factor F into a process control system controlling the rectification column (1000); (H) The set point TC of the control temperature (TC) is calculated from the first reference temperature (T1) measured during the operation of the distillation column (1000) and the second reference temperature (T2) measured during the operation of the distillation column (1000). ｓｅｔｐｏｉｎｔ and calculating The method according to claim 1 or 2, wherein the following is performed:

8. 3. The method of claim 1, wherein component A comprises a mixture of 2,3-toluenediamine and 3,4-toluenediamine, and component B comprises a mixture of 2,4-toluenediamine and 2,6-toluenediamine.

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