Apparatus and method for separating a substance mixture

Abstract

The present invention relates to a rectification apparatus and to a method of separating a substance mixture S into at least three fractions A, B1 and C for recovery of a target product, wherein fraction B1 contains the target product and (at least) one constituent other than the target product, fraction C contains high boilers and fraction A contains low boilers, and fraction B1 is removed in gaseous form in a sidestream, and wherein the rectification apparatus comprises: a closed-loop control device (IX) for controlling the content of the constituent of fraction B1 other than the target product in said fraction, wherein the closed-loop control device (IX) comprises: a quality controller (IXa) comprising a measurement device for determining the content of the constituent of fraction B1 other than the target product in said fraction, wherein a target content for said content is stored in the quality controller, and a pressure controller (IXb) for closed-loop control of the pressure in an offgas conduit (120) upstream of an offgas control valve (200) by means of the offgas control valve, wherein a pressure target for said pressure is stored in the pressure controller, wherein the quality controller is set up such that it adjusts the pressure target in the event that a variance from the target content is established so as to counteract the variance. The invention further relates to a computer system for closed-loop control of the composition of fraction B1 obtained in the rectification apparatus according to the invention or by the method according to the invention, and to a computer program product for implementing the closed-loop control regime according to the invention.

Description

[0001] 2024PF30020 - Abroad

[0002] - 1 -

[0003] DEVICE AND METHOD FOR SEPARATION OF A MIXTURE OF MATERIALS

[0004] The present invention relates to a rectification device and a method for separating a mixture of substances S into at least three fractions A, Bl and C for obtaining a target product, wherein fraction Bl contains the target product and (at least) one component different from the target product, fraction C contains high-boiling substances and fraction A contains low-boiling substances, and fraction Bl is withdrawn in a side stream in gaseous form, and wherein the rectification device comprises a control device (IX) for controlling the content of the component different from the target product in fraction Bl in this fraction, wherein the control device (IX) comprises: a quality controller (IXa) comprising a measuring device for determining the content of the component different from the target product in fraction Bl in this fraction, wherein a target content for this content is stored in the quality controller.and a pressure regulator (IXb) for controlling the pressure present in an exhaust gas line (120) upstream of an exhaust gas control valve (200) via the exhaust gas control valve, wherein a setpoint pressure for this pressure is stored in the pressure regulator, and wherein the quality controller is configured such that, in the event of a detected deviation from the setpoint, it adjusts the setpoint pressure to counteract the deviation. The invention further relates to a computer system for controlling the composition of the fraction Bl obtained in the rectification device according to the invention or with the method according to the invention, and a computer program product for carrying out the control according to the invention.

[0005] If a mixture containing a low-boiling component (A), a medium-boiling component (B), and a high-boiling component (C) is to be separated by distillation, two columns are often necessary when using simple rectification columns without a partition; see Chemical Engineering and Processing 49 (2010) 139–146 [1]. For example (see Fig. 2(a) of [1]), the low-boiling component (A) can be separated overhead in the first rectification column. A bottoms product, essentially free of the low-boiling component, is obtained in the bottoms, which can then be further separated in a second column. The medium-boiling component (B) is obtained at the top and the high-boiling component (C) in the bottoms. Depending on the composition of the mixture to be separated and the separability of the individual components (i.e., their boiling point differences), the high-boiling component (C) can also be separated first in the bottom of the first column (see Fig. 2(b) of [1]).The mixture of light and medium-boiling components (A, B) obtained at the top is then separated in the second column. The light-boiling component (A) is obtained at the top, and the medium-boiling component (B) is obtained at the bottom.

[0006] In many cases, the use of a rectification column with at least one partition (hereinafter referred to as a partition column) is the more cost-effective alternative to the classic separation sequence with regard to investment and energy costs. With a partition column, all components can be separated in a single step (see Fig. 3 of [1]). This is made possible by a partition arranged in the middle part of the column, which creates a longitudinal division of the 2024PF30020 - Abroad

[0007] - 2 -

[0008] The column is designed to prevent cross-mixing of liquid and / or vapor streams. The mixture to be separated, also called the feed, must be added on the opposite side of the product outlet for the medium-boiling component (in the so-called feed section of the column). FIG. 3(c) of [1] shows a typical arrangement of the mass transfer elements, where structured packings are very frequently used. A common mass transfer element (also called the packing bed) is arranged above the partition. It serves to enrich the low-boiling component (A) by separating the medium-boiling component (B). Further mass transfer elements (packing beds) are arranged to the left and right of the partition. The bed below the feed is on the feed side, and the bed above the feed is on the side of the side outlet (the so-called side outlet).The withdrawal section of the column serves to separate the low-boiling component (A), preventing this component from reaching either the sidestream withdrawal for the medium-boiling component (B) or the area below the dividing wall. The bed above the feed on the feed side and the bed below the feed on the side withdrawal side each serve to separate the high-boiling component (C), with the aim of being as free as possible of component (C) in the area above the dividing wall and at the sidestream withdrawal for component (B). The shared bed in the lower part of the column serves to concentrate the high-boiling component (C). In contrast to a simple sidestream column without a dividing wall, the dividing wall column makes it possible to obtain the medium-boiling component (B) in high purity (i.e., largely or completely without admixtures of the high-boiling component (C) and the low-boiling component (A)); see also Chem. Eng. Technol.10 (1987) 92–98 [2], Nevertheless, there are also applications for simple side-stream columns without a partition; see, for example, DE 29 33 601 Al, which describes a process for the production of mixtures of diphenylmethane diisocyanate isomers and optionally 4,4-diphenylmethane diisocyanate with a low content of uretdiones and hydrolyzable chlorine compounds by distillation of a crude MDI mixture using (among other things) a side-stream column (10) without a partition. The decision as to whether the side stream should be withdrawn in liquid or gaseous form does not depend on whether a side-stream column is equipped with a partition or not.

[0009] A special type of longitudinally divided column is described in EP 1 112 769 Al. This document deals with the special case of extractive distillation. In extractive distillation, a high-boiling, non-volatile, miscible substance (the entrainer or extraction solvent) is added to a mixture of azeotropic or very low-boiling substances. This entrainer does not form an azeotrope with the substances to be separated. When separating a binary mixture, a first column typically separates the pure first substance into a mixture of the second substance and the extraction solvent. This mixture is then separated in a second column into the pure second substance and pure extraction solvent, which can be recycled back to the first column. EP 1 112 769 Al, however, describes the use of a column with a side draw-off, designed such that 2024PF30020 - Foreign

[0010] - 3 - the tasks of substance separation and extraction solvent purification can be carried out solely in this column, thus making a further column unnecessary. The described column has a main column section (3) consisting of two parallel chambers (1 in the feed section, 2 in the withdrawal section) below a feed device (4) for a mixture to be separated. The chamber (2) of the main column section (3) is closed at the top from the interior of the column. The closed design of the chamber (2) ensures that the component to be withdrawn in the withdrawal section only passes by the lower end of the longitudinal partition from the feed section to the withdrawal section and prevents extraction solvent fed in the upper part of the column from entering the withdrawal section. This is essential for the process according to EP 1 112 769 A1 and distinguishes the process described therein from simple (i.e.Non-extractive distillations take place in longitudinally divided columns (divided columns) that have a vertically open interior on both sides of the dividing wall. The column also includes a raffinate section (5) above the feed unit (4), a stripping section (7) below the main column section (3), and a sump (8) with associated sump heating (9). An extraction solvent (carrying solvent) is concentrated in the stripping section (7) of the column, drawn off from the sump (8), and fed back in above the raffinate section (5). A raffinate fraction is stripped from the solvent-containing liquid in a chamber (1) of the main column section (3) and concentrated to a high-purity raffinate in the upper raffinate section (5) before being withdrawn at the top of the column.From the other chamber (2) of the main column section (3), which is closed at the top relative to the column's interior and is designed as a rectification section with several theoretical separation stages, a high-purity extract is withdrawn as a vaporous side stream, condensed, and partially returned to chamber (2). A column with associated measuring and control devices for carrying out the process is also described. Examples of mixtures to be separated include aromatic / non-aromatic mixtures, olefin / paraffin mixtures, and olefin / paraffin / diolefin mixtures. Examples of suitable extraction solvents include sulfolane, N-methylpyrolidone, dimethylacetamide, acetonitrile, dimethyl sulfoxide, dimethylformamide, ethylene glycols, morpholine, N-substituted morpholines, water, and mixtures thereof.

[0011] EP 1 112 769 Al aims to provide a control system for the distillation process operated in the described column, ensuring a high purity corresponding to a specified value and a quantity of extract drawn off as a side draw-off corresponding to a specified value. To achieve this goal, it is proposed to measure the temperature in the chamber (2), which is closed at the top from the column interior, and to control it by adjusting the chamber pressure (P2) prevailing in this chamber (2). The described control system takes advantage of the fact that, in extractive distillation of narrow-boiling or azeotropic mixtures, the extraction solvents used have a significantly higher boiling point than the substances to be separated.

[0012] - 4 -

[0013] The temperature, preferably measured in the lower region of chamber (2), is a measure of the mixture composition in this region. If the temperature measurement deviates from a target value, this means that the steam flow entering chamber (2) from below also does not correspond to the design. A correction is made by changing the pressure level in chamber (2). The proposed solution is based on the understanding that the pressure (P2) in chamber (2), which is closed at the top from the column interior, can be changed relative to the column operating pressure (Pi), and that the pressure differences can be used to control the steam flows entering the parallel chambers. A pressure measuring and control device 24 is provided for controlling the chamber pressure P2.It features a pressure measuring device PRC, which is arranged in the side exhaust between a condenser 13' and a condensate collection tank 21', and further includes a pressure regulating valve 22'. The chamber pressure P2 is measured and regulated to correspond to a pressure setpoint. The pressure setpoint is variable and is used as a control variable for temperature control. Using a measuring device TRC connected to a lower section of chamber 2, the temperature is measured and regulated by controlling the pressure P2 prevailing in chamber 2. The temperature measuring device TRC and the previously described pressure regulating device PRC are connected in a control loop. If the temperature reading at the measuring point is greater than a temperature setpoint, a higher pressure setpoint is specified and the pressure level P2 in chamber 2 is increased by opening the regulating valve 22' (and vice versa).Changing the pressure level P2 in chamber 2 increases or decreases the vapor flow into this chamber. The described control is therefore tailored to the specific case of extractive distillation in a column specifically designed for extractive distillation and cannot be readily transferred to other separation applications. Potential applications of dividing wall columns outside the specialized field of extractive distillation in a single column are discussed below.

[0014] A typical application of the partition column technology described above is the purification of isocyanates; in particular, the separation of a mixture of isomers of methylenediphenyl diisocyanate (mMDI) into two medium-boiling product streams (Bl, B2) should be mentioned, namely a fraction Bl consisting essentially of 4,4'-mMDI and a fraction B2 consisting essentially of a mixture of 2,4'-mMDI and 4,4'-mMDI. Other components of the mMDI mixture are to be transferred to the low-boiling or high-boiling stream, depending on their boiling point. In such a separation task, the boiling point differences of the components to be separated are comparatively small, which is why temperature measurement provides only insufficient information about the composition of a mixture. Furthermore, a closed chamber as described in EP 1 112 769 Al would prevent the separation of low-boiling impurities. 2024PF30020 - Foreign

[0015] - 5 -

[0016] In the prior art, such a mixture of mMDI isomers to be separated is obtained by phosgenation of a mixture (MDA) of isomers of mMDA and its higher homologs, the polymethylenepolyphenylenepolyamines (pMDA), followed by work-up of the phosgenation product. After removal of excess phosgene, the co-product hydrogen chloride, and the solvent used in the phosgenation, the work-up includes a so-called "polymer separation" in which mMDI isomers are partially separated from the MDI by distillation. The distilled mMDI isomer mixture contains the three isomers 2,2'-mMDI, 2,4'-mMDI and 4,4'-mMDI (where the 2,2'-isomer is only present in small amounts and, as it is undesirable for most applications, is generally largely removed from the final product fractions) as well as low-boiling byproducts (such as phenyl isocyanate) and high-boiling components (such as...Small amounts of the higher homologs of mMDI, the so-called polymer-MDI (pMDI), are entrained. The separation of such an mMDI isomer mixture and, if necessary, fine purification of the resulting fractions has been described several times in the literature.

[0017] EP 1 561 746 A2 describes a process for producing mMDI fractions containing 2,4'-mMDI, in which the 2,2'-mMDI fraction is largely removed from the isomer mixture. In one embodiment of the process, 4,4'-mMDI is removed from the crude mMDI isomer mixture by distillation to a degree of 10% to 98%, followed by the separation of 2,2'-mMDI from the fraction thus obtained, yielding a fraction containing 0 to 0.4 wt% 2,2'-mMDI, 1 to 95 wt% 4,4'-mMDI, and 5 to 98.6 wt% 2,4'-mMDI. The steps of separating the 4,4'-mMDI and the 2,2'-mMDI can also be carried out simultaneously in a common distillation step in a sidestream column.

[0018] EP 1 686 112 Al describes a process for the production of 2,2'-mMDI-poor 2,4'-mMDI by distillation of a mixture of mMDI isomers, wherein at least one distillation stage uses a dividing wall column, wherein at least one mixture is obtained which contains 85 to 99 wt% 2,4'-mMDI, a maximum of 15 wt% 4,4'-mMDI and a maximum of 0.2 wt% 2,2'-mMDI.

[0019] CN 111 848455 A describes a process for the production of isocyanates with low coloration. The process comprises vacuum distillation in a dividing wall column with gaseous sidestream withdrawal and cooling of the withdrawn fraction in a heat exchanger. The sidestream of the dividing wall column has a control valve to regulate the flow rate. The application aims to prevent the formation of solid deposits on the control valve. To this end, the control valve should always be open to 50 to 80% during continuous operation and should not be actuated more than 8 times per month. To control the degree of opening and the actuation frequency of the control valve, a pressure equalization control valve is installed on the line leading from the heat exchanger to the vacuum unit. The setpoint of the differential pressure controller is determined by a level controller, which monitors the level in the sump of the 2024PF30020 - Foreign

[0020] - 6 -

[0021] The heat exchanger regulates the back pressure of the control valve. This back pressure can be adjusted by setting the opening degree of the pressure equalization control valve. The back pressure of the control valve, in turn, influences the required opening of the control valve at a specific operating load. This ensures that the opening of the control valve is greater than 50% at minimum operating load.

[0022] WO 2012 / 066001 A1 describes a process for the purification of mixtures containing 4,4'-mMDI, comprising the distillative purification of a mixture I containing 4,4'-mMDI by means of a column Kl, wherein the gaseous stream consisting of the mixture I in the column Kl is brought into contact with at least one liquid compound A having the same or a higher boiling point than 4,4'-mMDI, and wherein the gaseous stream O obtained at the top of the column containing 4,4'-mMDI is cooled to a temperature of 20 °C to 60 °C in a maximum of 5 seconds. In a preferred embodiment, the mixture I, which is fed to column Kl, originates from a second column K2, in which crude mMDI is completely or partially separated into its isomers, preferably by completely or predominantly separating 4,4'-mMDI from the isomers 2,4'-mMDI and / or 2,2'-mMDI. Column K2 is preferably a dividing wall column.The procedure is intended to reduce the formation of derivatives, in particular the formation of dimeric derivatives (such as uretdiones and uretonimines).

[0023] GB 1,413,074 also aims to reduce dimers, proposing to rapidly cool the stream of evaporated isocyanate produced in a distillation by spraying in liquid isocyanate.

[0024] US 9,035,087 B2 discloses a process for producing a polyisocyanate comprising a purification step of an unpurified polyisocyanate. This purification step includes a step for removing tar components (polyisocyanate residue) and a step for distilling the tar-free polyisocyanate in a dividing-wall column. A comparative example illustrates that, in the distillation of toluene diisocyanate (TDI), replacing the dividing-wall column with a simple side-stream column without a dividing wall results in a product with increased acidity and deteriorated color. The patent does not provide details on controlling the operation of the distillation column, regardless of whether it is configured as a dividing-wall column or a simple side-stream column without a dividing wall.

[0025] In connection with the purification of TDI, EP 3 556 745 Al, also published as US 2020 / 377447 Al, describes a process that aims to minimize the dimer content in the final product. The process involves separating and purifying TDI by feeding a mixture containing TDI as a major component into a reactive partition column equipped with a condenser and an evaporator, maintaining a condenser pressure of 66.6 mbar or less and a condenser temperature of 130°C or less. 2024PF30020 - Foreign

[0026] - 7 - a total pressure difference in the reactive dividing wall column of a maximum of 53.3 mbar is maintained and a residence time of the reaction mixture in the reactive dividing wall column of 10 seconds to 150 seconds is maintained.

[0027] The purification of amines in a dividing wall column is also known. EP 1 746 083 A1 describes a process for the production of meta-toluenediamine comprising the distillative separation of crude toluenediamine obtained by hydrogenation of dinitrotoluene in a dividing wall column. At least four product streams, PI to P4, are obtained, wherein product stream PI is a stream containing a low-boiling component, product stream P2 is a stream containing o-toluenediamine, product stream P3 is a stream containing m-toluenediamine, and product stream P4 is a stream containing a high-boiling component and m-toluenediamine.

[0028] CN 116 943 264 A describes an automatic control method for the rectification of an isocyanate in a rectification column with gaseous withdrawal of a product stream. The rectification column comprises a pressure equalization valve on a pressure equalization line that connects a heat exchanger, which is connected to a side line of the rectification column, to a vacuum system, as well as a protective gas supply line connected to the pressure equalization line between the heat exchanger and the pressure equalization valve, wherein the protective gas supply line is equipped with an inert gas flow control valve. The automatic control method regulates the liquid level of the heat exchanger by means of separate control loops for adjusting the opening degrees of the pressure equalization valve and the inert gas flow control valve, with switching between the two control loops being performed by a logic controller.The described process is intended to enable the production of isocyanates with a low color number.

[0029] When separating a mixture into three to four product streams (low-boiling stream (A), one or two medium-boiling streams (B), and high-boiling stream (C)) in a column with a side draw, preferably, but not necessarily, in a dividing wall column, the fundamental objective is to obtain each product stream with as close as possible to the desired composition, i.e., the carryover of other components must be avoided as much as possible. Often, the goal is to isolate a target product from a mixture containing components with lower and higher boiling points than the target product in the purest possible form. In such a case, in a column with a side draw, the target product is obtained as the medium-boiling fraction (Bl) withdrawn from the side, while the lower and higher-boiling components should be transferred as completely as possible to the low-boiling fraction (A) (the overhead product) or to the high-boiling fraction (C) (the bottoms product). 2024PF30020 - International

[0030] - 8 -

[0031] The target product is typically specified in such a way that the proportion of components other than the target product must not exceed a certain limit. In industrial practice, control systems are used for this purpose, which automatically take measures to counteract any deviation from the specification as quickly as possible. Such deviations can occur in the operation of a rectification column, particularly when certain parameters change significantly within a short period. Examples include changes in the composition and flow rate of the feed. Both of these can alter the composition of the target product stream, to which the control system must react quickly to ensure that the product always meets specifications or that periods of production of defective batches are at least minimized.A control system like the one described in the aforementioned patent application CN 111 848455 A will reach its limits here. For example, significant changes in the operating conditions of the rectification unit often require strong responses from the control system, even to the point of requiring responses that are incompatible with the operating conditions of the control valve disclosed in the aforementioned patent application CN 111 848455 A. This, in turn, can negatively affect product quality (in addition to the impact on quality caused by the change in operating conditions). Therefore, a device / method that eliminates the need for a control valve in the connecting line of the side draw-off between the column and the heat exchanger would be advantageous.The aforementioned procedure according to CN 116 943 264 A does not require such a control valve, but it does require complex logic control and a constant (i.e., not just temporary) nitrogen flow.

[0032] Therefore, there was a need for further improvements in the purification and / or isomer separation of isocyanates and other products such as amines, which can serve as precursor compounds of isocyanates. In particular, it would be desirable to ensure sufficient quality control of the target product even with abrupt changes in input parameters such as the composition and flow rate of the feed, in order to obtain it at a consistently high purity, thus making further purification as unnecessary as possible.

[0033] Taking this need into account, the present invention provides the following:

[0034] In a first aspect, the invention relates to a rectification device for separating a mixture of substances S into at least three fractions A, Bl and C for obtaining a target product (optionally several, in particular two, target products), wherein the fraction Bl is the target product and (at least) one component different from the target product, 2024PF30020 - Abroad

[0035] - 9 - fraction C contains components with a higher boiling point than the target product (so-called "high-boiling substances"; also, if applicable, some portions of the target product itself) and fraction A contains components with a lower boiling point than the target product (so-called "low-boiling substances"; also, if applicable, some portions of the target product itself), and wherein the rectification apparatus comprises the following equipment:

[0036] (I) a rectification column, in particular having an interior space open throughout in the vertical direction, wherein a feed unit for the mixture S is attached to the side of the rectification column,

[0037] (II) a bottom evaporator for heating a liquid bottom product obtained from the mixture S,

[0038] (III) a sampling unit for extracting fraction C from the liquid bottoms product,

[0039] (IV) a top condenser for condensing a gaseous top product obtained from the mixture S (where the top condenser may be located inside or outside the rectification column),

[0040] (V) a recycling and withdrawal unit for recycling a first part of the overhead product condensed in the overhead condenser into the rectification column and for withdrawing a second part of the overhead product condensed in the overhead condenser as fraction A from the rectification column,

[0041] (VI) a first vacuum system connected to the overhead condenser via a first exhaust line (110), comprising (at least) a vacuum generating device for receiving non-condensable components of the overhead product,

[0042] (VII) a side outlet arranged on the rectification column for the gaseous withdrawal of the Bl fraction,

[0043] (VIII) a side-draw condenser for liquefying the gaseous fraction Bl withdrawn, wherein the side-draw condenser has a second exhaust line (120) equipped with an exhaust control valve (200), wherein the second exhaust line is connected to the first vacuum system or a different second vacuum system which also includes (at least) a vacuum generating device, and wherein the second exhaust line is connected to the side draw-off on the gas side, wherein preferably no device is provided for returning a portion of the liquefied fraction Bl obtained in the side-draw condenser to the rectification column, and

[0044] (IX) a control mechanism for regulating the content of the non-target component of fraction Bl in that fraction (i.e. in fraction Bl), wherein the control mechanism comprises: 2024PF30020 - Foreign

[0045] - 10 -

[0046] (a) a quality controller comprising a measuring device for (periodic or continuous) determination of the content of the component of the Bl fraction other than the target product in that fraction (i.e. in the Bl fraction), wherein a target content for that content is stored in the quality controller, and

[0047] (b) a pressure regulator for controlling the pressure present in the second exhaust gas line upstream (i.e. upstream in the direction of flow) the exhaust gas control valve via (at least) the exhaust gas control valve, wherein a pressure setpoint for this pressure is stored in the pressure regulator, wherein the quality regulator is configured to adjust the pressure setpoint in such a way as to counteract a detected deviation from the setpoint.

[0048] In a second aspect, the invention relates to a method for separating a mixture of substances S into at least three fractions A, Bl and C for obtaining a target product (optionally several, in particular two, target products), wherein the method preferably does not include extractive distillation, and wherein fraction Bl contains the target product and (at least) one component different from the target product, fraction C contains components with a higher boiling point than the target product (so-called "high-boiling substances"; also optionally proportions of the target product itself), and fraction A contains components with a lower boiling point than the target product (so-called "low-boiling substances"; also optionally proportions of the target product itself), wherein the method is carried out using the rectification apparatus according to the invention, and wherein the method comprises the following steps:

[0049] (1) Distilling the mixture S in the rectification column (I), producing a liquid bottoms product which is heated by means of the bottoms evaporator (II) and wherein fraction C is withdrawn from the liquid bottoms product, wherein fraction Bl is withdrawn in gaseous form from the rectification column in the side draw (VII) and fed to the side draw condenser (VIII) (in particular without influencing the flow of fraction Bl by changing the 2024PF30020 - Foreign

[0050] - 11 -

[0051] Position of a valve, if present, in the line from the rectification column to the side-draw-off condenser), and wherein a gaseous overhead product is produced, which is condensed by means of the overhead condenser (IV) and partly returned to the rectification column and partly withdrawn as fraction A from the rectification column, wherein non-condensable portions of the overhead product are directed into the first vacuum system (VI), and

[0052] (2) Condensing the gaseous fraction Bl withdrawn in the side-draw-off condenser (VIII) to obtain a liquefied fraction Bl and a non-condensable gas phase, wherein the non-condensable gas phase is directed via the second exhaust line (120) into the first or second vacuum system, wherein preferably no part of the liquefied fraction Bl is returned to the rectification column, wherein

[0053] (3) the content of the component of the Bl fraction other than the target product is determined (periodically or continuously) and, if a deviation from the target content of the component of the Bl fraction other than the target product is detected, the deviation is counteracted by adjusting the pressure setpoint for the pressure present in the second exhaust gas line upstream (i.e. upstream in the direction of flow) the exhaust gas control valve.

[0054] In a third aspect, the invention relates to a computer system for controlling the composition of the fraction Bl obtained in the rectification device according to the inventive method, comprising: an interface unit configured to read (periodically or continuously) the content of the component of fraction Bl that differs from the target product; a processor configured to compare the (periodically or continuously) read content of the component of fraction Bl that differs from the target product with the predetermined target content stored in and retrievable from a database communicatively linked to the processor; and, in the event of a deviation from the predetermined target content, to adjust the pressure setpoint for the pressure present in the second exhaust gas line upstream (i.e., in the flow direction upstream) of the exhaust gas control valve in such a way as to counteract the deviation. 2024PF30020 - Foreign

[0055] - 12 - In a fourth aspect, the invention relates to a computer program product comprising instructions which, when the computer program product is executed by the computer system according to the invention, cause it to execute step (3) of the method according to the invention.

[0056] The attached illustrations show:

[0057] FIG. 1 shows a possible embodiment of a rectification device according to the invention;

[0058] FIG. 2 shows the course of the content of 2,4'-mMDI in fraction Bl ("2.4 PV") during a sudden change in the composition of the feed under the conditions of Examples 2a, 3a and 4a;

[0059] FIG. 3 shows the content of 2,4'-mMDI and 4,4'-mMDI ("4.4 PV") of fraction B2 ") during a sudden change in the composition of the feed under the conditions of Examples 2a, 3a and 4a;

[0060] FIG. 4 shows the course of the content of 2,4'-mMDI in fraction Bl during a sudden change in the flow rate of the feed under the conditions of examples 2b, 3b and 4b;

[0061] FIG. 5a shows the content of 2,4'-mMDI of fraction B2 during a sudden change in the feed flow rate under the conditions of Examples 2b, 3b and 4b; and FIG. 5b shows the content of 4,4'-mMDI of fraction B2 during a sudden change in the feed flow rate under the conditions of Examples 2b, 3b and 4b.

[0062] Within the description of the invention, formulations such as "whereby a target value for this content is stored in the quality controller" and "whereby a pressure setpoint for this pressure is stored in the pressure controller" are used. This terminology refers to a storage of the respective setpoint in such a way that the respective controller can access it. In practice, the "storage" of the respective setpoint can, for example, take place in a database connected to a process control system that controls the operation of the rectification device according to the invention and all its control devices (and possibly other devices). This is encompassed by the aforementioned formulations and does not exceed the scope of the present invention.

[0063] The term distillation, as used in the context of the present invention, also includes rectification.

[0064] The term "vertically open interior of the rectification column" refers to a design of the column interior such that a material flow in a vertical direction is ensured over the entire height of the rectification column (and not by impermeable closures or the like, as in the case of 2024PF30020 - Foreign).

[0065] - 13 - closed chamber 2 in EP 1 112 769 Al, is prevented). The presence of usual column internals such as liquid collectors and liquid distributors, mass transfer elements such as packings, and the like is of course not excluded by this. In the case of a dividing wall column, the expression "open interior space throughout in the vertical direction" means that a mass flow in the vertical direction is ensured on both of the at least one dividing wall (i.e., over the entire column cross-section) over the entire height of the rectification column.

[0066] The following is a brief summary of various possible embodiments of the invention:

[0067] In a first embodiment of the rectification device according to the invention, which can be combined with all other embodiments (unless these necessarily provide for several vacuum systems), the second exhaust gas line is connected to the first (in this embodiment only) vacuum system.

[0068] In a second embodiment of the rectification device according to the invention, which is a special embodiment of the first embodiments, the first (in this embodiment only) vacuum system has (at least) one exhaust gas condenser (400) upstream of the (at least one) vacuum generating device, wherein the connection of the second exhaust gas line to the first exhaust gas line is upstream of the (at least one) exhaust gas condenser.

[0069] In a third embodiment of the rectification device according to the invention, which is a special embodiment of the second embodiments, the rectification device has facilities for combining fraction A with components of the overhead product liquefied in the exhaust gas condenser.

[0070] In a fourth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, a vertical partition (at least, preferably exactly) is arranged in the rectification column. This partition does not extend to the lower boundary of the rectification column (marked "X" in FIG. 1) nor to the upper boundary of the rectification column (marked "Y" in FIG. 1), but is therefore only located in the central region of the rectification column. The partition divides the rectification column into an inlet section on the feed unit side and an outlet section on the side of the side outlet. The inlet and outlet sections are, in particular, open at both the top and bottom (i.e., the interior of the rectification column is completely open in the vertical direction, as described above, on both sides of the partition).

[0071] In a fifth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the 2024PF30020 - Abroad comprises

[0072] - 14 -

[0073] Rectification device with a cooler (Villa) for further cooling of the fraction Bl. liquefied in the side exhaust condenser.

[0074] In a sixth embodiment of the rectification device according to the invention, which is a special embodiment of the fifth embodiment, the cooler is arranged in such a way that a part of the further cooled fraction Bl obtained in it is returned to the side extraction condenser.

[0075] In a seventh embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the side-extraction condenser is a heat exchanger designed for steam generation.

[0076] In an eighth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the sump evaporator is a circulating evaporator.

[0077] In a ninth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the measuring device of the quality controller is configured to carry out the determination of the content of the component of fraction Bl that differs from the target product in this fraction (i.e. in fraction Bl) at least lx per minute.

[0078] In a tenth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the rectification device is set up to separate the mixture S into four fractions A, Bl, B2 and C, wherein the fraction B2 contains a further target product and wherein, for the purpose of, in particular liquid, withdrawal of the fraction B2, a further side draw-off is arranged above the side draw-off for the gaseous withdrawal of the fraction Bl of the rectification column.

[0079] In an eleventh embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the quality regulator is configured so that, in the event of a detected exceedance of the target content, it increases the pressure setpoint (so that, as a result, the pressure regulator reduces the valve opening of the exhaust gas control valve) and, in the event of a detected fall below the target content, it decreases the pressure setpoint (so that, as a result, the pressure regulator increases the valve opening of the exhaust gas control valve).

[0080] In a twelfth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the rectification device has a (so-called "feedforward") control device comprising measuring devices for the (periodic or continuous) determination of the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the flow of the mixture (S), wherein the control device is configured such that, in 2024PF30020 - Abroad

[0081] - 15 -

[0082] Dependence of the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the flow of the mixture (S), which additionally adjusts the pressure setpoint specified by the quality controller (disturbance feedforward).

[0083] In a thirteenth embodiment of the rectification device according to the invention, which is a special embodiment of the twelfth embodiment, the measuring devices of the control device are configured to carry out the determination of the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the determination of the flow of the mixture (S) at least lx per minute.

[0084] In a fourteenth embodiment of the rectification device according to the invention, which can be combined with all other embodiments, the side exhaust condenser or the second exhaust gas line (120) has an inert gas supply line equipped with an inert gas control valve (300) at a position located (in the direction of flow) upstream of the exhaust gas control valve (200) (in particular as close as possible to the connection of the second exhaust gas line to the side exhaust condenser), wherein the pressure regulator is configured to also regulate the pressure present in the second exhaust gas line upstream (i.e. upstream in the direction of flow) the exhaust gas control valve via the inert gas control valve (so that the pressure regulator can additionally react to a change in the pressure present in the second exhaust gas line upstream (i.e. upstream in the direction of flow) the exhaust gas control valve by a corresponding change in the valve opening of the inert gas control valve).

[0085] In a fifteenth embodiment of the rectification device according to the invention, which can be combined with all other embodiments (except those in which the mixture (S) is not an isocyanate fraction), the mixture (S) is an isocyanate fraction that is obtained in the production of an isocyanate (after at least partial separation of any solvent that may be used).

[0086] In a sixteenth embodiment of the rectification device according to the invention, which is a special embodiment of the fifteenth embodiment, the isocyanate fraction comprises xylylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate or methylenediphenylene diisocyanate.

[0087] In a seventeenth embodiment of the rectification device according to the invention, which is a special embodiment of the sixteenth embodiment, the target product is xylylene diisocyanate and the component of fraction Bl other than the target product is chloromethylbenzyl isocyanate, or the target product is 1,5-pentane diisocyanate and the component of fraction Bl other than the target product is 1,5-pentane chloroisocyanate, or the target product is 1,6-hexane diisocyanate and the component of fraction Bl other than the target product is 1,6-hexane chloroisocyanate, or 2024PF30020 - Abroad

[0088] - le is the target product 4,4'-methylenediphenylene diisocyanate and the component of the fraction Bl 2,4'-methylenediphenylene diisocyanate that differs from the target product.

[0089] In an eighteenth embodiment of the rectification device according to the invention, which can be combined with all other embodiments (except those in which the mixture (S) is not an amine fraction), the mixture (S) is an amine fraction that is obtained in the production of an amine (after at least partial separation of any solvent that may be used).

[0090] In a nineteenth embodiment of the rectification device according to the invention, which is a special embodiment of the eighteenth embodiment, the amine fraction comprises toluenediamine.

[0091] In a twentieth embodiment of the rectification device according to the invention, which is a special embodiment of the nineteenth embodiment, the target product is meta-toluenediamine, and the component of the fraction Bl that differs from the target product is ortho-toluenediamine.

[0092] In a twenty-first embodiment of the rectification device according to the invention, which is a particular embodiment of the seventeenth and twentieth embodiments, the target content of the component of fraction Bl that differs from the target product in this fraction (i.e. in fraction Bl) is 2.0 wt%, preferably 1.0 wt%, particularly preferably 0.5 wt%, most preferably 0.1 wt%, based on the total mass of fraction Bl.

[0093] In a first embodiment of the method according to the invention, which can be combined with all other embodiments, the content of the component of fraction Bl that differs from the target product is determined in this fraction (i.e. in fraction Bl) at least lx per minute.

[0094] In a second embodiment of the process according to the invention, which can be combined with all other embodiments, the mixture S is separated into four fractions A, Bl, B2 and C, wherein the fraction B2 contains a further target product and wherein, for the purpose of, in particular liquid, withdrawal of the fraction B2, a further side draw-off is arranged above the side draw-off for the gaseous withdrawal of the fraction Bl of the rectification column.

[0095] In a third embodiment of the method according to the invention, which can be combined with all other embodiments, the pressure setpoint is adjusted in such a way that, if an overshoot of the setpoint is detected, the pressure setpoint is increased (so that, as a result, the pressure regulator reduces the valve opening of the exhaust gas control valve) and 2024PF30020 - Abroad

[0096] - 17 - if a shortfall in the target content is detected, the target pressure value is reduced (so that, as a result, the pressure regulator increases the valve opening of the exhaust control valve).

[0097] In a fourth embodiment of the method according to the invention, which can be combined with all other embodiments, the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the flow of the mixture (S) is determined (periodically or continuously), wherein, depending on the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the flow of the mixture (S), the pressure setpoint is additionally adjusted (disturbance feedforward).

[0098] In a fifth embodiment of the method according to the invention, which is a special embodiment of the fourth embodiment, the content of the component of the fraction Bl in the mixture (S) that differs from the target product and / or the flow of the mixture (S) is determined at least lx per minute.

[0099] In a sixth embodiment of the method according to the invention, which can be combined with all other embodiments, an inert gas is introduced into the side exhaust condenser or into the second exhaust gas line (120) at a position located upstream of the exhaust gas control valve (200) (in particular as close as possible to the connection of the second exhaust gas line to the side exhaust condenser), wherein the pressure present in the second exhaust gas line upstream (i.e. upstream in the flow direction) of the exhaust gas control valve is also adjusted by adjusting the inert gas supply.

[0100] In a seventh embodiment of the process according to the invention, which can be combined with all other embodiments (except those in which the mixture (S) is not an isocyanate fraction), the mixture (S) is an isocyanate fraction that is obtained in the production of an isocyanate (after at least partial separation of any solvent that may be used).

[0101] In an eighth embodiment of the process according to the invention, which is a special embodiment of the seventh embodiment, the isocyanate fraction comprises xylylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate or methylenediphenylene diisocyanate.

[0102] In a ninth embodiment of the process according to the invention, which is a particular embodiment of the eighth embodiment, the target product is xylylene diisocyanate and the component of fraction Bl other than the target product is chloromethylbenzyl isocyanate, or the target product is 1,5-pentane diisocyanate and the component of fraction Bl other than the target product is 1,5-pentane chloroisocyanate, or the target product is 1,6-hexane diisocyanate and the component of fraction Bl other than the target product is 1,6-hexane chloroisocyanate, or 2024PF30020 - Abroad

[0103] - 18 - is the target product 4,4'-methylenediphenylene diisocyanate and the component of the fraction Bl other than the target product is 2,4'-methylenediphenylene diisocyanate.

[0104] In a tenth embodiment of the process according to the invention, which can be combined with all other embodiments (except those in which the mixture (S) is not an amine fraction), the mixture (S) is an amine fraction that is obtained in the production of an amine (after at least partial separation of any solvent that may be used).

[0105] In an eleventh embodiment of the method according to the invention, which is a special embodiment of the tenth embodiment, the amine fraction comprises toluenediamine.

[0106] In a twelfth embodiment of the method according to the invention, which is a special embodiment of the eleventh embodiment, the target product is meta-toluenediamine, and the component of the fraction Bl that differs from the target product is ortho-toluenediamine.

[0107] In a thirteenth embodiment of the method according to the invention, which is a particular embodiment of the ninth and twelfth embodiments, the target content of the component of fraction Bl that differs from the target product in this fraction (i.e. in fraction Bl) is 2.0 wt%, preferably 1.0 wt%, particularly preferably 0.5 wt%, most preferably 0.1 wt%, based on the total mass of fraction Bl.

[0108] The embodiments and further possible configurations of the invention briefly described above are explained in more detail below. All embodiments described above and the further configurations of the invention described below are, unless the context clearly indicates otherwise to a person skilled in the art or unless expressly stated otherwise, freely combinable with one another. This also applies across category boundaries; for example, an embodiment described for the rectification device according to the invention is also applicable, mutatis mutandis, to the method according to the invention.

[0109] The rectification device and the method according to the invention are explained in more detail below with reference to FIG. 1. In the arrangement shown in FIG. 1, the rectification column (I) is a partition column, i.e., it has at least one, preferably exactly one, vertical partition inside the column body. However, the invention is not limited to such an embodiment. The control system according to the invention can also be used in side-stream columns without a partition. The section of a partition column relevant for the control system according to the invention can, from a process engineering perspective, also be considered an independent column without a partition. 2024PF30020 - Abroad

[0110] - 19 -

[0111] The mixture to be separated (S) is fed laterally into the rectification column (I) in the region of the partition. Generally (i.e., not only in the specific embodiment shown in FIG. 1), the partition divides the rectification column into a feed section on the feed unit side and a discharge section on the side of the side outlet, with the feed section and the discharge section each being open at the top and bottom (or, in other words, the rectification column has an interior space that is completely open in the vertical direction on both sides of the partition). The partition is located in the central region of the rectification column, i.e., it does not extend to either the lower boundary X or the upper boundary Y. In the embodiment shown in FIG. 1, a recirculating evaporator serves as the bottom evaporator (II), which is also generally preferred.The swamp fraction (C) is discharged via the extraction unit (III); the head fraction (A) via (V).

[0112] FIG. 1 shows a particularly preferred embodiment of the invention for the recovery of two fractions, Bl and B2, taken laterally in the region of the partition (on the side opposite the feed). In this embodiment, the rectification apparatus is configured to separate the mixture S into four fractions A, Bl, B2, and C, and the process is operated to recover these four fractions. Fraction B2 contains a further target product, and for the extraction of fraction B2, particularly in liquid form, a further side outlet is arranged above the side outlet (VII) for the gaseous extraction of fraction Bl on the rectification column. Compared to the more common liquid extraction of the side fraction in the prior art, the required evaporator capacity of the bottom evaporator is higher for gaseous extraction.This is offset by the advantage that gaseous extraction results in a higher purity of the Bl fraction with regard to its content of dimerized byproducts. The resulting simplification of subsequent processing (in particular the potential elimination of further rectifications) more than compensates for the disadvantage of the higher evaporator capacity.

[0113] In the arrangement shown in FIG. 1, the rectification column (I) is connected to a single vacuum system. Here, the second exhaust line (120) is connected to the "first" (in this embodiment: single) vacuum system (VI). It is preferred that the vacuum system (VI) has at least one exhaust condenser (400). This is located upstream of the at least one vacuum generating unit and thus protects it from liquid entrainment. As shown in FIG. 1, it is preferred that the second exhaust line (120) is connected to the first exhaust line (110) such that the connection of the two lines is located upstream of the exhaust condenser (or the first exhaust condenser in a series of exhaust condensers) in the flow direction.

[0114] The second exhaust pipe (120) is connected on the gas side to the side exhaust (VII) via the side exhaust condenser (VIII), which is designed as a heat exchanger (the second exhaust pipe (120) is therefore connected to it above the sump level of the heat exchanger (VIII). This ensures that the pressure in the second exhaust pipe is equal to the pressure in the 2024PF30020 - Abroad

[0115] - 20 -

[0116] The side outlet (VII) is coupled to the pressure in the rectification column (I). When the pressure in the second exhaust line (120) increases, more gas remains in the rectification column (I), which – with a time delay – increases the reflux ratio of the column and improves the separation efficiency.

[0117] The heat released during the condensation of the overhead product in the overhead condenser (IV) can be used to generate steam (2), as shown in FIG. 1, for example in a tube bundle heat exchanger supplied with cooling water (1).

[0118] Preferably, the rectification device has facilities for combining fraction A with the components liquefied in the exhaust gas condenser (not shown in FIG. 1).

[0119] The gaseous fraction Bl is liquefied in the side-draw condenser (VIII). It is preferred to design the side-draw condenser (VIII) as a heat exchanger for steam generation. It is further preferred, as shown in FIG. 1, to feed the fraction (Bin.) liquefied in the side-draw condenser to a cooler (Villa) for further cooling. In the arrangement shown in FIG. 1, the side-draw condenser (VIII) and the cooler (Villa) form a so-called quenching circuit: The liquefied portion of the Bl fraction is drawn from the sump of the side-draw condenser (VIII) and, via the cooler (Villa), shown here as a heat exchanger, is partly pumped back into the side-draw condenser (VIII) and partly withdrawn as a liquid product stream (Blfi.,p).The extraction of the liquid product flow is determined via a level indicator control (LIC) to prevent the side extraction condenser from running full or empty.

[0120] The liquefaction and, if necessary, further cooling of the gaseous fraction Bl should be carried out as quickly as possible to prevent undesirable subsequent reactions of the gaseous product stream Bl. This can be achieved in various ways; the arrangement shown in FIG. 1 is exemplary and not to be understood as limiting.

[0121] The quality controller (IXa) used to regulate product quality comprises, in addition to the actual control unit (QIC (Quality Indicator Control)), a measuring device (in FIG. 1, a near-infrared measuring device; NIR). This measuring device of the quality controller (IXa) is preferably configured, and the method is preferably operated, such that the determination of the content of the component of fraction Bl that differs from the target product is carried out at least lx per minute in this fraction (i.e., in fraction Bl). The type of measuring principles that can be used is, of course, not limited to NIR; other analytical methods known in the field, such as MIR (mid-infrared spectroscopy), Raman spectroscopy, or gas chromatography, can also be used.

[0122] It is particularly preferred to use such a quality controller (IXa) and to operate the process in such a way that 2024PF30020 - Abroad

[0123] - 21 - if the target content of the component of fraction Bl other than the target product is detected in this fraction (i.e. in fraction Bl), the pressure setpoint is increased (so that, as a result, the pressure regulator reduces the valve opening of the exhaust control valve), and if the target content of the component of fraction Bl other than the target product is detected in this fraction (i.e. in fraction Bl), the pressure setpoint is decreased (so that, as a result, the pressure regulator increases the valve opening of the exhaust control valve).

[0124] The quality controller (IXa) is preferably configured as a so-called PID controller ("proportional-integral-derivative controller"). In particular, the quality controller is configured as a direct-acting controller that acts on the setpoint of the pressure controller (IXb; so-called PIC; "pressure indicator controller"). Direct control occurs when a process variable above the setpoint requires an increase in the actuator output.

[0125] In a preferred embodiment, also shown in FIG. 1, the side exhaust condenser (VIII) additionally has an inert gas supply line equipped with an inert gas control valve (300), through which an inert gas (3), preferably nitrogen, is introduced into the side exhaust condenser or – more preferably – into the second exhaust line (120) at a position located (in the direction of flow) upstream of the exhaust control valve (200) (in particular, as close as possible to the connection of the second exhaust line to the side exhaust condenser). The pressure regulator (IXb) is configured to regulate the pressure present in the second exhaust line (120) upstream of (i.e., in the direction of flow, upstream of) the exhaust control valve also via the inert gas control valve (300), so that the pressure regulator responds to a change in the pressure present in the second exhaust line upstream of (i.e.,The pressure present in the direction of flow (upstream of the exhaust gas control valve) can additionally react by a corresponding change in the valve opening of the inert gas control valve. In a preferred embodiment, a corresponding change in the valve opening of the inert gas control valve means that if the target concentration of the component of fraction Bl other than the target product is exceeded in this fraction, the valve opening of the inert gas control valve (300) is enlarged, and if the target concentration of the component of fraction Bl other than the target product is not reached in this fraction (i.e., in fraction Bl), the valve opening of the inert gas control valve (300) is reduced.

[0126] The supply of inert gas does not necessarily have to be continuous. For example, it may be advantageous to use this and the described additional control only during transient operating conditions, such as the start-up and shutdown of the rectification device or in the event of process disturbances. During normal operation, it is usually sufficient to use only the inventive control of the pressure present in the second exhaust gas line upstream (i.e., upstream in the flow direction) of the exhaust gas control valve (200). Both control systems form a robust "cascade control" that compensates for typical short-term operating disturbances (e.g., of the vacuum, flow rates, etc.) through the internal regulator (pressure regulator).

[0127] - 22 -

[0128] Temperatures, etc.) are eliminated by means of a precise control parameter setting, and the concentration of the product is ensured by the external controller (quality controller) in the event of fundamental changes in the process parameters (e.g., in the content of the target product in the feed).

[0129] In a particularly preferred embodiment, the invention additionally comprises a so-called "feedforward" control system. Here, the rectification device has a control unit comprising measuring devices for the periodic or continuous determination of the content of the component of fraction Bl (different from the target product) in the mixture (S) and / or the flow rate of the mixture (S). The control unit is configured and the process is operated such that, depending on the content of the component of fraction Bl (different from the target product) in the mixture (S) and / or the flow rate of the mixture (S), the pressure setpoint specified by the quality controller is additionally adjusted (so-called disturbance variable feedforward). Changes in the input values ​​(concentration and / or flow rate) are detected in order to react to them at an early stage.The feedforward signal is applied to the output signal of the quality controller and directly affects the pressure setpoint. The feedforward signal calculates a fictitious pressure setpoint, which the quality controller then corrects. This effectively feeds disturbances into the quality controller using the input measurement signals.

[0130] It is preferred that the measuring devices of the control device are set up and the procedure is operated in such a way that the determination of the content of the component of the fraction Bl in the mixture (S) that is different from the target product and / or the determination of the flow of the mixture (S) is carried out at least lx per minute.

[0131] A control valve as described in CN 111 848455 A is unnecessary within the scope of the present invention. It may be advantageous to provide a shut-off valve in the side draw-off section (VII), i.e., in the line from the fraction Bl withdrawal point on the column body to the inlet of the side draw-off condenser (VIII). Such a shut-off valve can be used in certain special operating conditions with complete return flow, such as in temporary standby operation or during start-up and shutdown. However, it does not perform any control function for the actual production operation.

[0132] The rectification apparatus and the process according to the invention are particularly suitable for separating an isocyanate fraction (= mixture S) that is obtained in the production of an isocyanate after at least partial removal of a solvent that may be used. Suitable isocyanate fractions include, for example, xylylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexane diisocyanate, or methylenediphenyl diisocyanate. It is particularly preferred that the target product is xylylene diisocyanate and the component of fraction Bl other than the target product is chloromethylbenzyl isocyanate, or 2024PF30020 - Abroad

[0133] - 23 - the target product is 1,5-pentane diisocyanate and the component of the fraction Bl other than the target product is 1,5-pentane chloroisocyanate, or the target product is 1,6-hexane diisocyanate and the component of the fraction Bl other than the target product is 1,6-hexane chloroisocyanate, or the target product is 4,4'-methylenediphenylene diisocyanate and the component of the fraction Bl other than the target product is 2,4'-methylenediphenylene diisocyanate.

[0134] Of course, other components besides those explicitly mentioned may be present. For example, in the case of 4,4'-methylenediphenyl diisocyanate as the target product, trace amounts of phenyl isocyanate (PHI) and 2,2'-methylenediphenyl diisocyanate may be present.

[0135] For the aforementioned target products, the target content of the component of fraction Bl that is different from the target product in this fraction (i.e., in fraction Bl) is preferably 2.0 wt%, particularly preferably 1.0 wt%, very preferably 0.5 wt%, and extremely preferably 0.1 wt%, based on the total mass of fraction Bl.

[0136] The target product 4,4'-methylenediphenylene diisocyanate and the component of the fraction Bl, 2,4'-methylenediphenylene diisocyanate, which differs from the target product, are particularly preferred. In this case, the target product can be obtained with such purity (especially with regard to the dimer content) that further purification of the 4,4'-methylenediphenylene diisocyanate in a further rectification column is unnecessary. Processes for obtaining mixtures of substances (S) containing 4,4'-methylenediphenylene diisocyanate that are suitable for separation in the rectification column according to the inventive process are known. Such mixtures originate from the production of MDI (mixture of mMDI and pMDI) by phosgenation of the corresponding amines, a process that is well known. Usually, the mixture of mMDI and pMDI obtained in the production of the amines is phosgenated as such and thus converted into MDI.In the work-up of the MDI, after the removal of any solvent used, excess phosgene, and the co-product hydrogen chloride, a so-called polymer separation takes place, in which mMDI is distilled off, leaving behind a mixture of pMDI and mMDI with a reduced mMDI content compared to the crude product MDI. The distilled mMDI can serve as the mixture (S) of the present invention. The corresponding mixtures (S) generally contain, in addition to byproducts such as the aforementioned PHI and optionally small amounts of entrained pMDI, all three mMDI isomers (i.e., the 2,2'-, 2,4'-, and 4,4'-isomers). When these mixtures are separated according to the present invention, two fractions are preferably obtained: the fraction Bl, which contains 4,4'-methylenediphenylene diisocyanate as the target product, and the aforementioned fraction B2, which is a mixture of 2,4'-methylenediphenylene diisocyanate and 2024PF30020 - Abroad.

[0137] - 24 -

[0138] 4,4'-Methylenediphenylene diisocyanate, especially in a mass ratio in the range of 55 : 45 to 45 : 55, as a further target product.

[0139] The rectification apparatus and the method according to the invention can also be used to separate an amine fraction that arises in the production of an amine after at least partial removal of any solvent that may be used, e.g., to separate a toluenediamine-containing fraction. It is particularly preferred that the target product is meta-toluenediamine and that the component of fraction Bl other than the target product is ortho-toluenediamine. The desired content of ortho-toluenediamine in fraction Bl is preferably 2.0 wt%, particularly preferably 1.0 wt%, very preferably 0.5 wt%, and extremely preferably 0.1 wt%, based on the total mass of fraction Bl.

[0140] As already mentioned, the invention also relates to a computer system for controlling the composition of the Bl fraction obtained in the rectification device / method according to the invention, in order to ensure that it contains the target product in the highest possible purity. According to the invention, this computer system comprises at least the following: an interface unit configured to read (periodically or continuously) the content of the component of the Bl fraction that differs from the target product, and a processor configured to compare the (periodically or continuously) read content of the component of the Bl fraction that differs from the target product with the predetermined target content stored in and retrievable from a database communicatively linked to the processor, and, in the event of a deviation from the predetermined target content, to adjust the pressure setpoint for the second exhaust line before (i.e.,to adjust the pressure present in the direction of flow (in front of) the exhaust gas control valve in such a way as to counteract the deviation.

[0141] The invention further relates to a computer program product. This comprises commands which, when executed by the computer system according to the invention, cause the computer program product to perform step (3) of the method according to the invention – namely, the (periodic or continuous) determination of the content of the component of fraction Bl that differs from the target product, in conjunction with taking countermeasures in the form of adjusting the setpoint pressure for the pressure present in the second exhaust gas line upstream (i.e., in the flow direction upstream) of the exhaust gas control valve when a deviation from the setpoint is detected. 2024PF30020 - Foreign

[0142] - 25 -

[0143] The following examples were simulated on a computer using Honeywell's commercial software, UniSim Design.

[0144] Example 1: Simulation of a separation of substances in a steady state (according to the invention)

[0145] In a rectification apparatus for separating a mixture (S) of mMDI isomers, 4528 kg / h of the mMDI mixture is continuously fed into a rectification column (I) (packed column) configured as a dividing wall column. The mMDI mixture consists mainly of three mMDI isomers (2,2'-mMDI with a mass fraction of 1.1%, 2,4'-mMDI with a mass fraction of 16.3%, and 4,4'-mMDI with a mass fraction of 82.5%) and also contains residual amounts of high- and low-boiling by-products from the preceding process stages. The rectification column (I) is equipped with a bottom evaporator (II) and a top condenser (IV) and is connected to a single vacuum system. The mMDI mixture is fed into the rectification column (I) at the center of the column body. Rectification takes place under vacuum at a head pressure of 5.0 mbar, a sump temperature of 223 °C and a condensation temperature in the head condenser (IV) of 161 °C.Four factions will be retained.

[0146] Faction A

[0147] To remove traces of lighter substances from the mixture (S), a defined stream of approximately 100 kg / h is drawn off as fraction A from the column head distillate in the top condenser (IV) via a recirculation and withdrawal unit (V), and the remainder of the condensate is returned as reflux to the top packing of the rectification column (I). The withdrawal stream (fraction A) contains mainly lighter substances as well as a high proportion of 2,2'- and 2,4'-mMDI and flows into the so-called lighter substance receiver for further processing. The exhaust gas from the condensation is further condensed in a post-condenser (exhaust gas condenser) at lower temperatures and pressures to separate residual mMDI (approximately 57 kg / h) from the exhaust gas stream before it enters the vacuum generation unit of the vacuum system (VI) via a first exhaust gas line. The mMDI liquefied in the exhaust condenser is combined with the extraction stream from the head condenser in a common storage tank. 2024PF30020 - International

[0148] - 26 -

[0149] Factions Bl and B2

[0150] Two product streams are drawn off in the partition wall area of ​​the rectification column (I):

[0151] Below the first packing element (viewed from above), the entire liquid stream from the packing is collected in a liquid collector and drawn off from the rectification column (I) via a side drawoff. The stream is directed into a feed vessel and distributed from there. A portion is removed from the feed vessel as fraction B2, and a portion is returned to the rectification column (I) as reflux. The liquid fraction B2 is drawn from the feed vessel at a rate of approximately 1071 kg / h. It consists primarily of 2,4'-mMDI and 4,4'-MDI in a mass ratio of approximately 1.2:1 and contains less than 0.2 wt% 2,2'-mMDI.

[0152] Below the second packing element, a partial gas stream (fraction Bl) at a temperature of approximately 215 °C is drawn off from the rectification column (I) via a side draw-off (side draw-off (VII)) and condensed in a side draw-off condenser (VIII) at approximately 138 °C and approximately 13 mbar, and then further cooled to 45 °C. This further cooling to 45 °C is achieved using a so-called "quench cycle," in which the bottom stream of the side draw-off condenser (VIII) is cooled in a downstream condenser, and a portion of the cooled stream is withdrawn as the product fraction, while another portion is returned to the bottom of the side draw-off condenser (VIII). The exhaust gas produced during condensation is routed via a second exhaust gas line into the first exhaust gas line of the head condenser (IV), the second exhaust gas line being connected to the first exhaust gas line upstream of the exhaust gas condenser in the direction of flow and having an exhaust gas control valve.The gaseous fraction Bl is taken from the rectification column (I) at a rate of approximately 2996 kg / h. It contains approximately 1.5 wt% 2,4'-mMDI and 98.5 wt% 4,4'-mMDI.

[0153] Faction C

[0154] A bottom product (fraction C) containing mainly high-boiling by-products, 4,4'-mMDI and pMDI is withdrawn from the rectification column (I) via a withdrawal unit (III) at a rate of approximately 300 kg / h.

[0155] The extracted quantity of gaseous fraction Bl is controlled by precise pressure regulation in the second exhaust line (the exhaust line of the side condenser (VIII)), which simultaneously influences the internal gas and reflux volumes in the rectification column (I). For this purpose, the rectification unit has a control device (IX). 2024PF30020 - Foreign

[0156] - 27 -

[0157] The pressure is set by measuring and regulating the pressure in the exhaust line of the side condenser (VIII), with a pressure regulator (IXb) controlling the exhaust control valve in the second exhaust line. The setpoint of the pressure regulator is set to approximately 10 mbar, but is continuously adjusted by a quality regulator (IXa). This quality regulator (IXa) is installed in the line through which the condensed and cooled fraction Bl from the rectification unit is discharged. The quality regulator (IXa) ensures the desired product quality (2.4 mMDI content).

[0158] Particularly during transition phases in process operation, such as start-up or shutdown, the pressure control in the second exhaust gas line by the pressure regulator (IXb) can be further supported by a controlled nitrogen injection into the side condenser (VIII). For this purpose, the second exhaust gas line (120) is equipped with a nitrogen supply line at a location in the immediate vicinity of its connection to the side exhaust condenser (VIII). This supply line has an inert gas control valve, which the pressure regulator (IXb) can open or close further according to the current requirements. In normal operation, the inert gas control valve is closed and the exhaust gas control valve is partially open. The quantity of the condensed and cooled fraction Bl extracted from the rectification unit is regulated by a level controller of the side exhaust condenser (VIII).

[0159] Simulations of at

[0160] The control of the rectification device differs in the following examples only in the area of ​​the side discharge of fraction Bl. All other parts of the rectification device are controlled identically. The aim of the dynamic simulations is to demonstrate the advantages of the control concept according to the invention compared to alternative concepts with regard to product quality.

[0161] These simulation studies simulated two scenarios for the operation of the rectification device.

[0162] In scenario 1, a sudden change in the composition of the mixture (S) was simulated. The 2,4'-mMDI mass fraction was increased from 16.3% to 20.0%, the 2,2'-mMDI mass fraction was increased from 1.1% to 2.0%, and the 4,4'-mMDI mass fraction was decreased from 82.5% to 77.9%.

[0163] In scenario 2, an increase in the input mass flow rate of the mixture (S) from 4528 kg / h to 4656 kg / h was simulated (with the same composition as in the steady-state simulation of Example 1). 2024PF30020 - Abroad

[0164] - 28 - In Figures 2 to 5b, the progression of the mass fractions relevant to product quality in fractions Bl and B2 is shown:

[0165] FIG. 2 shows the course of the content of 2,4'-mMDI in fraction Bl ("2.4 PV") in scenario 1.

[0166] FIG. 3 shows the content of 2,4'-mMDI and 4,4'-mMDI ("4.4 PV") of fraction B2 in scenario 1.

[0167] FIG. 4 shows the course of the content of 2,4'-mMDI in fraction Bl in scenario 2.

[0168] FIG. 5a shows the content of 2,4'-mMDI of fraction B2 in scenario 2.

[0169] FIG. 5b shows the content of 4,4'-mMDI of fraction B2 in scenario 2.

[0170] The curve of the 2.4'-mMDI mass fraction ("2.4 PV") for fraction Bl is shown. The 2.4'-mMDI mass fraction is controlled by a quality controller at a predetermined setpoint (SP) of 0.015 (1.5 mass %).

[0171] The profile of the 2.4'-mMDI and 4.4'-mMDI mass fractions for fraction B2 is shown. The 2.4'-mMDI mass fraction is controlled by a quality controller at a predetermined setpoint (SP) of 0.55 (55% by mass). Withdrawal of the Bl faction and the quality of the

[0172] Product flow as described in Example 1

[0173] The figures show that the maximum deviations from the target values ​​of the quality controllers in this example remain below a mass fraction of 0.003 (FIG. 2) and 0.03 (FIG. 3), respectively, and that the deviations are largely corrected by the end of the 1100-minute simulation period. It can also be seen that the deviations are corrected without oscillations.

[0174] 2b: Scenario 2, gaseous extraction of the Bl fraction and the quality of the

[0175] Product flow as described in Example 1

[0176] Figures 4 and 5a, b show that in this simulation example, there is only a minimal influence on the qualities of fractions Bl and B2. The deviations from the target values ​​of the quality controllers are corrected towards the end of the 1100-minute simulation period. 2024PF30020 - Abroad

[0177] - 29 -

[0178] Example 3a: Scenario 1, liquid extraction of fraction Bl and regulation of the product stream quality via the ratio of return flow to product stream (comparison)

[0179] In contrast to the procedure described in Example 1, the Bl fraction is drawn from the rectification column in liquid rather than gaseous form. The liquid stream, at a temperature of approximately 214 °C, is fed into a feed vessel and circulated through it. A portion of the drawn stream is returned to the rectification column as reflux, while the remainder is discharged as product for further processing. The fill level of the feed vessel is measured and controlled via the total mass flow rate of the reflux and product streams. Furthermore, the quality of the product stream is adjusted by controlling the 2,4'-mMDI content in the side draw-off via the ratio of reflux to product stream. To implement the level and quality control, the reflux and product mass flow rates are measured and adjusted by means of flow controllers via control valves in the reflux and product stream lines.

[0180] Figures 2 and 3 show that the maximum deviations from the target values ​​of the quality controllers in this example exceed a mass fraction of 0.007 (Figure 2) and 0.07 (Figure 3), respectively, and that the deviations are not corrected towards the end of the 1100-minute simulation period. Furthermore, a fluctuating mass fraction profile can be observed for fraction B2.

[0181] Example 3b: Scenario 2, liquid extraction of fraction Bl and regulation of the product stream quality via the ratio of return flow to product stream (comparison)

[0182] The operation and control of the rectification column are carried out as described in Example 3a.

[0183] Figures 4 and 5a, b show that while this simulation example has only a minimal influence on the qualities of fractions Bl and B2, a fluctuating profile of the mass fractions can be observed. The deviations from the target values ​​of the quality controllers are essentially corrected by the end of the 1100-minute simulation period.

[0184] Example 4a: Scenario 1, gaseous extraction of fraction Bl and control of the product stream quality based on the procedure described in CN 111848455 A (comparison)

[0185] The side exhaust of the column is extracted in gaseous form at a temperature of approximately 215 °C and condensed in a condenser-cooler combination, then further cooled to approximately 45 °C. The condensed and cooled liquid stream is discharged as the product stream from the sump of the condenser-cooler combination. (The non-2024PF30020 - foreign)

[0186] - 30 - Condensable components are discharged via an exhaust pipe to a vacuum system. Therefore, unlike example 1, the further cooling of fraction Bl occurs without the aid of a quench circuit.

[0187] The extraction rate of the gaseous side exhaust is indirectly controlled via the pressure differential between the column's gas extraction line and the condenser. This pressure differential is determined by a control valve in the line between the column and condenser, and by a control valve in the exhaust line to the vacuum system. The setpoint of the differential pressure controller is determined by a level controller, which regulates the fill level in the sump of the condenser-cooler combination. The differential pressure controller primarily regulates the pressure differential via the control valve in the exhaust line. In the event of larger deviations from the setpoint, the pressure differential is additionally regulated by the control valve in the line between the column and the condenser-cooler combination. Control via this valve should be avoided whenever possible, and ideally, the valve should be open as wide as possible to prevent material buildup on it.The discharge rate is set via a quality controller that regulates the 2.4-mMDI mass fraction in the product stream. A flow controller, which acts on a control valve in the product flow line, is subordinate to the quality controller. The control system described here is similar in its effect to that described in CN 111 848455 A, but is implemented differently in detail due to the parameters of the simulation used.

[0188] Figures 2 and 3 show that the maximum deviations from the target values ​​of the quality controllers for fractions Bl and B2 in this example are approximately 0.01 (Fig. 2) and 0.04 (Fig. 3) by mass, respectively. These deviations are not resolved by the end of the 1100-minute simulation period.

[0189] 4b: Scenario 2, gaseous extraction of the Bl fraction and the quality of the

[0190] The operation and control of the rectification column are carried out as described in Example 4a.

[0191] Figures 4 and 5a, b show that the maximum deviation from the target value of the quality controller for fraction Bl in this example is approximately 0.005 by mass (Figure 4). The deviations from the target value of the quality controller for fraction B2 are less significant. Furthermore, a fluctuating pattern of mass fractions can be observed for both fractions. 2024PF30020 - Abroad

[0192] - 31 -

[0193] A comparison of Examples 2a to 4b shows that the examples according to the invention exhibit the smallest fluctuations in the product quality of fractions Bl and B2. Furthermore, in the examples according to the invention, the deviations are compensated for without oscillations. Similar effort was expended in setting the PID controller parameters for the different comparison concepts in order to obtain the best possible controller parameters.

[0194] In addition to the advantages in control quality described above, the rectification device / method according to the invention offers the advantage, compared to liquid extraction (Example 3a / b), that there are no long residence times of the Bl fraction in the liquid state at high temperatures. This prevents the formation of dimers and eliminates the need for a further processing step using another rectification device.

[0195] In comparison to Example 4a / b, the rectification device / method according to the invention offers the advantage that the control valve in the gas extraction line between the rectification unit and the condenser-cooler unit can be omitted. The control valve has the disadvantage that deposits can form there, particularly with a small opening and / or through continuous adjustment of the control valve's opening degree. This problem is completely avoided in the method / concept / process according to the invention, since a control valve is not required.

Claims

1. 2024PF30020 - Abroad - 32 - 1. Rectification apparatus for separating a mixture of substances S into at least three fractions A, Bl and C for obtaining a target product, wherein fraction Bl contains the target product and a component different from the target product, fraction C contains components boiling at a higher boiling point than the target product and fraction A contains components boiling at a lower boiling point than the target product, and wherein the rectification apparatus comprises the following devices: (I) a rectification column, wherein a feed unit for the mixture S is attached to the side of the rectification column, (II) a bottom evaporator for heating a liquid bottom product obtained from the mixture S, (III) a sampling unit for extracting fraction C from the liquid bottoms product, (IV) a top condenser for condensing a gaseous top product obtained from the mixture S, (V) a recycling and withdrawal unit for recycling a first part of the overhead product condensed in the overhead condenser into the rectification column and for withdrawing a second part of the overhead product condensed in the overhead condenser as fraction A from the rectification column, (VI) a first vacuum system connected to the overhead condenser via a first exhaust line, comprising a vacuum generating device for receiving non-condensable components of the overhead product, (VII) a side outlet arranged on the rectification column for the gaseous withdrawal of the Bl fraction, (VIII) a side-extraction condenser for liquefying the gaseous fraction Bl, wherein the side-extraction condenser has a second exhaust line equipped with an exhaust control valve, wherein the second exhaust line is connected to the first vacuum system or a different second vacuum system which also includes a vacuum generating device, and wherein the second exhaust line is connected to the side-extraction condenser on the gas side, and (IX) a control device for regulating the content of the component of fraction Bl in that fraction other than the target product, the control device comprising: 2024PF30020 - Abroad - 33 - (a) a quality controller comprising a measuring device for determining the content of the component of the Bl fraction other than the target product in that fraction, wherein a target content for that content is stored in the quality controller, and (b) a pressure regulator for controlling the pressure present in the second exhaust gas line upstream of the exhaust gas control valve via the exhaust gas control valve, wherein a pressure setpoint for this pressure is stored in the pressure regulator, wherein the quality regulator is set up in such a way that, in the event of a detected deviation from the setpoint, it adjusts the pressure setpoint in such a way as to counteract the deviation.

2. Rectification apparatus according to claim 1, in which a vertical partition is arranged in the rectification column.

3. Rectification device according to claim 1 or 2, comprising a cooler (Villa) for further cooling of the fraction Bl. liquefied in the side draw-off condenser.

4. Rectification apparatus according to one of the preceding claims, wherein the rectification apparatus is configured to separate the mixture S into four fractions A, Bl, B2 and C, wherein fraction B2 contains a further target product and wherein a further side draw-off is arranged above the side draw-off for gaseous withdrawal of fraction Bl of the rectification column for the purpose of withdrawing fraction B2.

5. Rectification device according to one of the preceding claims, in which the quality controller is configured such that, in the event of a detected exceedance of the target content, it increases the pressure setpoint and, in the event of a detected fall below the target content, it decreases the pressure setpoint.

6. Rectification device according to one of the preceding claims, wherein the rectification device has a control device comprising measuring devices for determining the content of the component of fraction Bl other than the target product in the mixture (S) and / or the flow of the mixture (S), wherein the control device is configured to additionally adjust the pressure setpoint specified by the quality controller depending on the content of the component of fraction Bl other than the target product in the mixture (S) and / or the flow of the mixture (S). 2024PF30020 - Abroad - 34 - 7. Rectification device according to one of the preceding claims, in which the side exhaust condenser or the second exhaust line has an inert gas supply line provided with an inert gas control valve at a position located upstream of the exhaust control valve, wherein the pressure regulator is configured to also regulate the pressure present in the second exhaust line upstream of the exhaust control valve via the inert gas control valve.

8. A method for separating a mixture of substances S into at least three fractions A, Bl and C to obtain a target product, wherein fraction Bl contains the target product and a component different from the target product, fraction C contains components boiling at a higher boiling point than the target product and fraction A contains components boiling at a lower boiling point than the target product, wherein the method is carried out using a rectification apparatus according to any one of claims 1 to 7, and wherein the method comprises the following steps: (1) Distilling the mixture S in the rectification column (I), producing a liquid bottoms product which is heated by means of the bottoms evaporator (II) and wherein fraction C is withdrawn from the liquid bottoms product, wherein fraction Bl is withdrawn as a gas from the rectification column in the side draw (VII) and fed to the side draw condenser (VIII), and wherein a gaseous overhead product is produced which is condensed by means of the overhead condenser (IV) and partly returned to the rectification column and partly withdrawn as fraction A from the rectification column, wherein non-condensable portions of the overhead product are directed into the first vacuum system (VI), and (2) Condensing the gaseous fraction Bl extracted in the side exhaust condenser (VIII) to obtain a liquefied fraction Bl and a non-condensable gas phase, wherein the non-condensable gas phase is directed via the second exhaust line into the first or second vacuum system, wherein 2024PF30020 - Abroad - 35 - (3) the content of the component of fraction Bl other than the target product is determined and, if a deviation from the target content of the component of fraction Bl other than the target product is detected, the deviation is counteracted by adjusting the pressure setpoint for the pressure present in the second exhaust gas line upstream of the exhaust gas control valve.

9. The method according to claim 8, wherein the mixture S is separated into four fractions A, Bl, B2 and C, wherein fraction B2 contains a further target product and wherein a further side draw-off is arranged above the side draw-off for gaseous withdrawal of fraction Bl of the rectification column for the purpose of extracting fraction B2.

10. Method according to claim 8 or 9, wherein the pressure setpoint is adjusted such that, in the event of a detected exceedance of the target content, the pressure setpoint is increased and, in the event of a detected fall below the target content, the pressure setpoint is decreased.

11. Method according to one of claims 8 to 10, wherein the content of the component of fraction Bl other than the target product in the mixture (S) and / or the flow of the mixture (S) is determined, wherein, depending on the content of the component of fraction Bl other than the target product in the mixture (S) and / or the flow of the mixture (S), the target pressure is additionally adjusted.

12. Method according to one of claims 8 to 11, wherein an inert gas is introduced into the side exhaust condenser or into the second exhaust line at a position located upstream of the exhaust control valve, wherein the pressure present in the second exhaust line upstream of the exhaust control valve is also adjusted by adjusting the inert gas supply.

13. Rectification apparatus according to any one of claims 1 to 7 or method according to any one of claims 8 to 12, wherein the mixture (S) is an isocyanate fraction obtained in the production of an isocyanate, or wherein the mixture (S) is an amine fraction obtained in the production of an amine.

14. Computer system for controlling the composition of the fraction Bl obtained in a rectification device according to one of claims 1 to 7 or 13 or in a method according to one of claims 8 to 13, comprising: an interface unit configured to read the content of the component of the fraction Bl that differs from the target product, 2024PF30020 - Abroad - 36 - a processor configured to compare the read content of the component of fraction Bl that differs from the target product with the specified target content stored in and retrievable from a database communicatively linked to the processor, and in case of a deviation from the specified target content, to adjust the pressure setpoint for the pressure present in the second exhaust gas line before the exhaust gas control valve in such a way as to counteract the deviation.

15. Computer program product comprising instructions which, when the computer program product is executed by the computer system according to claim 14, cause the computer system to execute step (3) of the method according to any one of claims 8 to 13.

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