CN101386584A - Method for controlling production process - Google Patents

Abstract

The present invention provides a method for controlling a production process, such as an isocyanate production process, by a production facility having at least two feed streams, b) at least one bleed stream and c) at least one internal recycle stream, the production process being controlled by adjusting the amount of at least one feed stream by means of an adjustment controller to control the concentration and/or amount of the bleed stream.

Description

Method for controlling production process

This application is a continuation-in-part application of prior application No.11/638,817 filed on 14.12.2006 and claiming the benefit of said prior application.

Technical Field

The present invention relates to a production facility, such as an isocyanate production facility, and a method of controlling a production process comprising at least one internal recycle stream. The method easily optimizes the whole process in terms of the quantity and quality of the product, and reduces the production cost.

Background

In known isocyanate production facilities, a phosgene solution and an amine solution are introduced into a reactor where the phosgene and amine react to form isocyanate. The reaction products are usually separated in a distillation column to obtain purified isocyanates and often further purified in a distillation or crystallization unit to separate their isomers. To ensure that a predetermined amount of isocyanate is produced, the amount of phosgene and amine introduced into the reactor and/or column is controlled. Further, in order to ensure that isocyanate is produced which meets predetermined quality requirements, the process parameters of the reactor, such as pressure and temperature, are controlled. The distillation column used for separating off the materials in the reacted reaction mixture is designed so that the isocyanate separated off in this column can be obtained in the required quantity and quality from the reacted reaction mixture. The optimal process parameters of the isocyanate production process in a stable state can be calculated. These calculated process parameters are used as controlled variables to automatically keep them relatively stable in the event of an unstable disturbance. In general, it is possible to control each controlled variable independently of the other variables. For example, when the temperature of the distillation column decreases due to cold weather, the heating amount of the distillation column is increased to keep the optimum reference temperature of the distillation column stable.

In order to influence the chemical equilibrium of the reactor contents and to maximize the yield of isocyanate, it is preferred to supply an excess of phosgene to the reactor. Since phosgene is a highly toxic and harmful gas, excess phosgene must be removed after the reaction is completed. Instead, excess phosgene may be recycled to the reactor, thus increasing cost efficiency. The solvent obtained in the distillation step may also be recycled. However, the use of recycled phosgene and solvent may cause the isocyanate production process to become unstable. Since inevitable variations in process parameters affect the amount, pressure, temperature, concentration (quality), etc. of phosgene and solvent recycled, variations in process parameters and disturbances may increase instead when trying to automatically control the process parameters. Due to the recycling, almost every process parameter affects almost all other process parameters. Therefore, a certain number of reference parameters must be set manually based on the overall situation to avoid large-scale variations in the quantity and quality of the product isocyanates. Since large-scale variations in the quality of the isocyanate product are possible, conservative reference parameters are set for the isocyanate production process to ensure minimum quality of the isocyanate. This results in a difficult and complicated process control and high costs.

It is an object of the present invention to facilitate process control of production processes, in particular isocyanate production processes. A further object is to reduce the variation of products, such as isocyanates, thereby increasing the yield of products and reducing the production costs. In addition, it is also an object to improve and/or increase the automation of the production process. It is another object of the present invention to increase the stability of automated process control while preferably reducing the amount of unused reactants, such as phosgene, and used solvent. Furthermore, the amount of undesired substances in the production process should be reduced.

Disclosure of Invention

The above object is achieved by the process according to the invention for controlling a production process, in particular an isocyanate production process. In the production process controlled according to the invention, more than one feed stream, at least one draw stream and at least one internal recycle stream are used. In an isocyanate production process, the feed streams typically comprise: (1) a phosgene stream consisting essentially of phosgene and (2) a solvent feed stream consisting essentially of solvent. In addition to some plant-wide adjustment controls, controls for the amount of phosgene stream and solvent feed stream are included, providing adjustments to the exit stream concentration and quantity.

Drawings

FIG. 1 is a schematic simplified block diagram of an isocyanate production facility.

FIG. 2 is a schematic simplified block diagram of an isocyanate production process of an isocyanate production facility.

FIG. 3 is a schematic simplified block diagram of the facility illustrated in FIG. 2 with a monitoring or master controller.

Fig. 4 is a schematic simplified detail of the installation illustrated in fig. 3 with an adjustment control.

Fig. 5 is a schematic simplified detail of the installation illustrated in fig. 3 with another regulating control.

Fig. 6 is a schematic simplified detail of the installation illustrated in fig. 3 with another regulating control.

Fig. 7 is a schematic simplified detail of the installation illustrated in fig. 3 with another example of a regulating control.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The invention relates to a control method of a production process. Although the present invention can be applied to any production process, a production process for isocyanates will be described in more detail.

In the production of isocyanates according to the invention, more than one feed stream, at least one discharge stream and at least one internal recycle stream are used. The feed stream comprises: (1) a phosgene stream consisting essentially of phosgene and (2) a solvent feed stream consisting essentially of solvent. In addition to some plant-wide adjustment controls, controls for the amount of phosgene stream and solvent feed stream are included, providing adjustments to the exit stream concentration and quantity.

It has surprisingly been found that setting the amounts of phosgene stream and solvent feed stream as the main control variables of the plant results in an optimization of the whole plant range, when all other units of the isocyanate production facility are preferably controlled independently of each other. Therefore, a 2 × 2 system is sufficient for plant wide optimization. Other process parameters of the controlled process are of lesser importance for the optimization, since their influence on the composition of the draw stream is lower than the influence of the amounts of phosgene and solvent on it. Thus, the different subsystems of the isocyanate production process can be controlled independently of each other. In this way, it is possible to achieve a partial automation of each subsystem in which the reference variables can be determined by means of calculated and optimized process parameters. The relationship between the phosgene stream and the solvent feed and discharge streams results in simplified control of the production process, since the number of variables that need to be checked by a control system of complex setup is significantly reduced. Other process parameters are automatically set by the control method according to the invention. Since the process of the invention reduces the quantitative and qualitative (concentration) variations of the discharge streams, it is possible to produce improved isocyanate yields using improved reference parameters. Because substantially all of the unused solvent and phosgene can be recovered by the internal recycle stream, the amount of phosgene and solvent purged can be minimized and production costs reduced. In addition, the control method is stable according to the Nyquist criterion.

In a preferred embodiment of the invention, a phosgene stream is fed to a solution plant to produce a phosgene solution stream. A second stream of amine and solvent mixture (hereinafter referred to as the amine solution stream) is mixed with the phosgene solution stream. The content of amine in the amine solution stream is greater than or equal to 15% and less than or equal to 95%, preferably greater than or equal to 15% and less than or equal to 85% by weight, based on the total weight of solvent and amine in the amine solution stream. The phosgene content in the phosgene solution stream is > 15%, preferably > 20% and most preferably > 30% by weight, based on the total weight of solvent and phosgene in the stream. The ratio of the amine solution stream and the phosgene solution stream provides at least a stoichiometric amount of phosgene to react with the amino groups present in the amine solution stream. That is, there is one mole of phosgene per mole of amino groups in the amine solution stream. Preferably, an excess of phosgene based on amino groups present in the amine solution stream is provided; that is, there is more than one mole of phosgene for each mole of amino groups present in the amine solution stream.

The combined stream is fed to a reactor. The reactor is equipped to be able to accommodate at least one internal recycle stream, for example a recycle stream consisting essentially of phosgene and/or solvent and/or HCl. A recycle stream and a product stream are produced in the reactor, the product stream being predominantly isocyanate and, optionally, solvent. The product stream is separated from the reaction mixture by a separator into at least one effluent stream composed predominantly of isocyanate and at least one stream composed predominantly of solvent. The solvent feed stream is fed to the recycle stream in a recovery unit for recovering phosgene, and the recovery stream is fed from the recovery unit to the solution unit. The several streams may be fed directly or indirectly (e.g., through another stream, device, or sub-device) to its designated device.

It was surprisingly found that controlling the solution plant as a monitor resulted in control over the entire plant. Treating the solution plant as a key plant to optimize the overall plant footprint results in a simplified control concept that is easy to design and, if desired, adapt to changing conditions. For the recovery unit, the controlled amount of the solvent feed stream is a reference variable, while for the solution unit, the controlled amount of the phosgene stream is a reference variable.

Where the apparatuses other than the solution apparatus, such as the reactor, the separation apparatus, the recovery apparatus, etc., are controlled virtually independently of one another, the quantity and quality (concentration) of the discharge stream containing the desired product can be determined by calculation on the basis of the quality, temperature and level of the solution apparatus, i.e. essentially from the parameters determined in situ. These other devices (i.e., devices other than solution devices) may be controlled by setting pressures, temperatures, and/or levels based on the concentration and/or amount of their output streams. Further, the level may be controlled by feed forward control based on the amount of feed flow. Additional adjustment controls may also be used. For example, the viscosity of one of the at least one discharge stream can be controlled by adjusting the pressure and temperature of the separation device or sub-device.

Surprisingly, the control of the phosgene stream and the solvent feed stream produces an almost steady state reaction in the reactor, although recycling of phosgene, dissolving in the solution unit and mixing with dissolved amine takes place before the phosgene and solvent streams are fed to the reactor. Since the required quantity and quality of the draw stream is known, the conditions required for the separation device can be calculated, which in turn can be calculated for the reactor and for the solution device controlled by the main process control according to the invention. In a typical mode of operation, the mass of the effluent stream is determined by the reaction equation and the amount of isocyanate produced is determined by the amount of amine in the amine stream. The yield of the isocyanate production process therefore depends on the preset flow rate (amount) of the amine. The weight ratio of solvent to amine in the combined stream may be 10 or less, preferably 8 or less, most preferably from 2 to 7.

The method can be driven automatically and automated through control of the solution device. Disturbances that are not eliminated in the solution installation can be detected quickly, so that the regulating controls of the following installations (e.g. reactor and/or separation installation (separator)) can be pre-regulated to eliminate any possible effects of these disturbances. It is also preferred that substantially all devices and/or sub-devices are pre-conditioned when it is known that interference will occur. For example, when the output of the draw stream will vary, the appropriate amount of amine can be calculated and the control of the units and/or sub-units of the isocyanate production facility can be suitably pre-adjusted (e.g., adjusted levels, temperatures, etc.) to eliminate predictable interference and prevent exceeding upper or lower limit values. The controller is pre-adjusted to accommodate anticipated changes in conditions, resulting in improved stability.

Each of the units or sub-units used in the isocyanate production may be integrated into a single plant. For example, the solution means may be a separate solution tank or it may be integrated into the recovery means as the bottom of the absorber or the like. Further, each device or sub-device may be comprised of multiple sub-devices arranged in series and/or parallel to achieve a desired effect or function. For example, the reaction may be carried out in several steps in different reactors connected to each other. If necessary, the separation can also be carried out in different sub-units of the separation device to increase the quality of the separated streams. In case a device is composed of several sub-devices, each sub-device may have its own regulation controller. The regulating controls of the entire installation are preferably regulated so that the different subsystems all operate under optimum conditions. For example, the very low level in the first subsystem is prevented from occurring while the very high level in the second subsystem is prevented from occurring by the control of the entire apparatus. The feed and output streams to these units remain unchanged while the internal streams to the units are changed to conserve energy, steam, cooling, etc., and thereby increase, for example, thermal efficiency.

In order to control the isocyanate production process and the process parameters of the subsystems of this process, the following control concept can be implemented by means of a suitably designed controller: continuous feedback control, discontinuous feedback control, disturbance feedforward, load feedforward, selection of lower/upper limits, single variable controller, multivariable controller, advance/retard control, modeling control, selection of controller and control structure, interaction (RGA ═ relative gain permutation), directionality (SVD ═ decomposition of singular values), state estimator, online simulation, state controller, parameter validation, internal model control, model predictive control, gain permutation, single input multiple output control, range control, overload control, multiple input single output control, mixed value control, multiple input multiple output control, distributed control, disconnect, adaptive control, disturbance compensation, disturbance controller, cascade controller, single variable PID controller (PID controller ═ proportional-integral-derivative controller), anti-drift control, a configuration converter, a prefilter, a proportional control, a split-range control, a dead-time controller, a single variable P (P) and PI (PI) controller, and a signal filter. Preferably, a combination of simple and complex control concepts and/or partial automation concepts is used.

The process described can be used for the production of various organic isocyanates. The isocyanate may be MDI, i.e. one isocyanate or a mixture of two or more isocyanates of the diphenylmethane series as described by the following formula:

the isocyanate may also be TDI, i.e. toluene 2, 4-diisocyanate, toluene 2, 6-diisocyanate or a mixture of toluene 2, 4-diisocyanate and toluene 2, 6-diisocyanate; HDI, i.e., 1, 6-hexamethylene diisocyanate; or IPDI (isophorone diisocyanate).

The starting amine may be MDA, i.e. one amine or a mixture of two or more amines of the diphenylmethane series as described by the following formula:

the starting amine may also be TDA, i.e., 2, 4-diaminotoluene, 2, 6-diaminotoluene or a mixture of 2, 4-diaminotoluene and 2, 6-diaminotoluene; HDA, i.e., 1, 6-hexamethylenediamine; or IPDA (isophorone diamine).

The solvent may be selected from any known aliphatic, aromatic or araliphatic hydrocarbon, chlorinated aliphatic, aromatic or araliphatic hydrocarbon (e.g. chlorobenzene (MCB) or 1, 2-dichlorobenzene (ODB)), and any other solvent known in the art as a phosgenation solvent for amines, or mixtures comprising two or more of the above solvents.

The reactor used to complete the isocyanate forming reaction may include additional subsystems to ensure the desired quality. The separator is preferably a distillation apparatus, which may comprise more than one distillation step. The separator, particularly for purifying a solvent, may comprise a condensing unit (e.g. a stripping column). The recovery unit may comprise one or more condensers and one or more absorbers, due to the better solubility of phosgene in the solvent at lower temperatures and higher pressures. Further, the recovery device may be sealed by an inert gas (e.g., helium). The effluent stream may be connected to a post-treatment device. The isocyanate in the effluent stream can be further treated by means of a work-up unit. For example, the isocyanate can be divided into a stream consisting essentially of the isocyanate polymer and a stream consisting essentially of the isocyanate monomer isomers.

Each flow path may consist of one or more sub-devices, such as a surge tank, heat exchanger, valves, cooler, heater, condenser, and stream inlet. In order to collect sufficient information for automatic control, each device and each flow path may include sensing devices for determining process parameters such as temperature, pressure, concentration (mass), flow rate, level, feed rate, and discharge rate. Furthermore, each device and each flow path may comprise suitable control means (controllers) to control the measured process parameter by influencing, preferably directly, the controlled process parameter.

In a preferred embodiment of the invention, the change in solvent feed flow is adjusted to be proportional to the target amount of phosgene stream calculated based on the amount of amine feed stream. The ratio is determined by the concentration of the phosgene solution through the feedback controller. The solvent feed stream is adjusted prior to and/or faster than the targeted change in the amount of phosgene stream. In addition, the amount of solvent feed stream is adjusted based on the recycled phosgene stream. This control preserves the stability of the solution plant control. It has been surprisingly found that the level and concentration of the solution plant is related in a non-linear manner to the amount of phosgene stream and to the amount of solvent feed stream. A change of the relevant direction may even occur. For example, one increase in solution flow may increase the solution plant level and another decrease the solution plant level. This non-linear dependence renders stable control of the solvent apparatus almost impossible, or at least very complicated, since much information has to be processed in order to control the solution apparatus. However, it has been found that this non-linearity depends on the amount of recycled solvent. Since the control is based on the correlation between the amount of phosgene stream and the amount of solvent feed stream, the nonlinear effects of the recycled solvent can be compensated for. This control strategy enables a stable control by a controller that is easy to design and can be implemented using general methods known to those skilled in the art.

Preferably, the amount of solvent feed stream is adjusted in proportion to the amount of phosgene in the recycle stream and the amount of phosgene produced. The amount of phosgene in the recycle stream is calculated using the amount of phosgene stream over time, the amount and concentration of the mixture stream over time, and the reaction kinetics of the reactor. Due to the use of these control strategies, changes in the amount of phosgene in the recycle stream and the production of phosgene can be effected very rapidly. The precalculation of the amount of light can lead to a better prediction of the desired state in the recovery device. These knowledge makes it possible to pre-adjust the amount of solvent feed stream, thereby preventing or at least reducing unstable kinetics in the production process. Since the reaction kinetics and the number and concentration of the mixture streams are given, it is in most cases sufficient to store the measured number of phosgene streams in a storage device for calculating good correcting variables for the solvent feed stream, so that the phosgene to be purged is minimized. Changes in these process parameters over time may also be stored if changes in the quantity and concentration of the mixture stream are desired.

Since the recycle stream leads to strong interactions between the process units/sub-units, the amount of phosgene in the recycle stream and the concentration of solvent in the recycle stream preferably remain unchanged. Temperature and pressure regulation controls for the recycle stream may be used to minimize such interactions and disturbances.

Preferably, the solution set-up consists of more than one solution set-up controller. The first solution plant controller includes a solvent concentration controller associated with a change in the number of solvent feed streams in the solution plant, a solution temperature controller, for example, by controlling the heat exchanger(s), and a solution plant level controller associated with a change in the number of phosgene streams. The second solution plant controller includes a solvent concentration controller in the solution plant associated with changes in the number of phosgene streams and a solution plant level controller associated with changes in the number of solvent feed streams. The ratio used to calculate the solvent concentration change and the solution plant controller level depends on the frequency of the solvent feed stream quantity change and/or the phosgene stream quantity change. At lower frequencies, e.g., near steady state, the proportion of the first solution device controller is higher, while at higher frequencies, e.g., under disturbance, the proportion of the second solution device controller is higher. It has been found that the first solution plant controller is more stable at low disturbance frequencies, while the second solution controller is more stable at high disturbance frequencies. For this reason, stability is increased by taking this frequency dependence into account. The non-linear relationship between solvent feed flow and solution plant level must also be considered when designing the controller and selecting the control structure. Because the channels of these control problems are all strongly coupled together, a multivariable controller or similar control structure is preferred. Depending on the frequency, the multivariable controller adapts the gain and amplitude of the control action from the manipulated variable to the controlled variable.

To increase cost efficiency and/or reduce byproduct concentrations, it is important to reduce purge streams, such as phosgene purges. Typically, these purges may be absent or present in minor amounts in the process. Preferably, the amount of phosgene and HCl purged is controlled by the temperature of the recovery unit. It has been found that the temperature can be controlled independently of the concentration and level control of the phosgene solution. This makes the control easy to design and stable. Most preferably, control of the contingency event is provided for the phosgene purge to protect the purged phosgene and HCl from being neutralized or eliminated more than may be possible in an associated neutralization/elimination device. For this reason, after the first predetermined amount of purged phosgene has been exceeded, the amounts of phosgene stream and solvent feed stream are controlled to adjust the amount of purged phosgene to a level below the second predetermined amount of purged phosgene. The main control strategy according to the general operation of the present invention, in which the amount of phosgene flow and the amount of solvent feed flow can be controlled to adjust the concentration and level of the recovery unit or solution tank, which in turn controls the bleed stream, can be overridden for a while until the amount of purged phosgene is reduced to an acceptable value. In general, any emergency operation is brief, so that its disturbance on the quantity and quality of the outflowing stream is low or can even be compensated by other sub-units of the production process.

Preferably, the phosgene is produced on-site at an isocyanate production facility. Thus, a phosgene production unit for providing a phosgene stream may be included in the isocyanate production facility. The phosgene production plant can be composed of a CO stream consisting predominantly of CO and predominantly of Cl₂Cl of composition₂The streams are fed. CO and Cl₂And can also be produced on site. For example, Cl₂Can be produced by electrolysis of brine and/or aqueous HCl, or by the deacon process, i.e., by oxidation of gaseous HCl with oxygen or an oxygen-containing gas (e.g., air) using a catalyst. CO can be produced by using a reformer or by partial oxidation of coke. Most preferably, a control strategy for a phosgene production plant is provided which prevents as far as possible free Cl in the phosgene stream₂Is generated. Thus, in the event chlorine is detected in the phosgene stream, the amount of phosgene stream and/or the amount of CO stream and/or Cl₂The amount of the stream is controlled independently of the target amount of phosgene used in the reactor.

In order to reduce dynamic effects that may lead to large scale disturbances, it may be advantageous to provide a buffer, such as a tank connected to the flow path. Preferably, the buffering effect provided by the isocyanate production process subsystem is used. For example, a distillation column provides a buffering effect because the level (i.e., the ratio of liquid to gaseous components) of the distillation column is variable, so that more or less feed can be stored in the distillation column simply by closing or opening the output valve. Therefore, it is preferred to provide level controllers in at least part of the devices of the sub-system, such as the recovery device and/or the reactor and/or the separator. The level controller comprises a standard level controller and an interference level controller, which is amplified more strongly with respect to the standard level controller. The level controller is based on the interference level controller when the first predetermined upper limit level is exceeded and/or the first predetermined lower limit level is below the target. The level controller is based on a standard level controller when the second predetermined upper limit level is below the target and/or exceeds the second predetermined lower limit level. Thus, it is possible that the production of a given subsystem or subsystem plant segment is almost constant, unaffected by feed disturbance fluctuations. This ensures that the production can be slowly changed to a new optimum when the feed amount changes to another amount. At the same time it is also ensured that the subsystem or segments of the subsystem do not idle or overflow due to slow regulation, since the increase of amplification and the occurrence of production corrections are more rapid both when the upper limit is exceeded and when the lower limit is undershot. Since the solvent can be fed into the solvent feed stream as well as the amine solution stream, the resource stream comprising mainly the solvent is preferably fed into the solvent feed stream and/or the amine solution stream via a buffer tank.

A simplified version of the isocyanate production process is shown in figure 1. In fig. 1, the isocyanate plant 2 comprises an internal recycle stream 4. Several feed streams 6 are fed to the isocyanate plant 2. The feed stream 6 may consist of an amine, a solvent or phosgene. Several outlet streams 8 leave the isocyanate installation 2. The draw stream 8 can consist of the desired product (i.e. isocyanate), which can be provided in different qualities. For example, one draw stream 8 may consist of monomeric isocyanates having a specific structure, while the other draw stream 8 may consist of a mixture of isocyanates having different molecular weights. Additional output streams (e.g., purge) not illustrated in fig. 1 may also be provided. Due to the internal recycle stream 4, the control of the isocyanate plant 2 and of the isocyanate production process through the isocyanate plant 2 is very difficult, since almost every process parameter has an influence on the quantity and quality of the discharge stream 8.

The isocyanate production process is illustrated in more detail in figure 2 and will be described by way of example for the production of MDI (diphenylmethane diisocyanate) by reacting phosgene (COCl2) with MDA (diphenylmethane diamine) dissolved in MCB (monochlorobenzene). In the MDI production process shown in FIG. 2, the CO stream 10 and Cl₂Stream 12 is fed to phosgene generation unit 14. A phosgene stream 16 is fed from the phosgene generation unit 14 to a solution unit 18 where the phosgene is dissolved in the MCB. A phosgene solution stream 20 is fed from the solution unit 18 to a reactor 22. An amine solution stream 24 consisting of MDA dissolved in MCB is fed into the phosgene solution stream 20 before the combined stream 200 enters the reactor 22. It is also possible to feed the feed stream 24 directly into the reactor 22. It is also possible that the reactor 22 consists of more than one sub-unit, so that MDI can be prepared in more than one step. Will consist essentially of MDI and MCBA product stream 30 of composition is supplied from reactor 22 to a separator unit 32. The separator 32 may be composed of several sub-devices (not illustrated in fig. 2 for clarity) in series and/or parallel. The first effluent stream 38 from the separator 32 exits the production system for transport or storage. The first draw stream 38 consists essentially of polymeric MDI, i.e. a mixture of isocyanates of the diphenylmethane series as described by the general formula:

the second effluent stream 40 from separator 32 consists essentially of monomeric MDI, i.e., the diphenylmethane series isocyanate mixture described above where x ═ 2. To obtain monomeric MDI, the second effluent stream 40 is fed to an isomer separation device 42. The isomer separation unit 42 may be comprised of several subsystems connected in series and/or parallel to further separate the monomeric MDI isomers. A third effluent stream 48 and a fourth effluent stream 49, each consisting essentially of a specific monomeric MDI isomer (mdpi), exit the production system.

The recycle stream 50 from reactor 22 consists primarily of excess phosgene, solvent, HCl, and inert materials from the reactor. Recycle stream 50 is fed to recovery unit 52. Thus, the recycle stream 50 is an internal recycle stream in the isocyanate production process. In recovery unit 52, most of the phosgene is dissolved in the MCB fed to recovery unit 52 from solvent feed stream 54. Phosgene and impurities or by-products such as HCl that are not dissolved in the feed MCB exit recovery unit 52 by way of phosgene purge 56 to be eliminated. The recovered phosgene leaves recovery unit 52 in recovery stream 58 and is fed to solution unit 18. It is also possible to supply a recycle stream to stream 20 and/or reactor 22.

Although not necessary, it is preferred that the stream is fed indirectly to its designated device where the structural design of the isocyanate facility can allow. For example, in FIG. 2, an indirect feed of phosgene stream 16 is illustrated. If the phosgene generation device 14 is located near the recovery device 52, it may be preferable to feed the phosgene of the phosgene stream 16 to the recovery device 52, the recycle stream 50, and/or the resource stream 62, so that the phosgene stream is fed indirectly to the solution device 18. Those skilled in the art will readily recognize other advantageous possibilities for indirect feeding of further streams. For example, the solvent feed stream 54 may be first fed into a buffer tank 66, and so on.

The weight ratio of amine to solvent in stream 200 entering reactor 22 is preferably 10 or less, preferably 2 or more and 8 or less, and most preferably 2 or more and 7 or less. The amine content of the amine solution stream 24 is ≥ 15% and ≤ 95%, preferably ≥ 15% and ≤ 85% by weight, based on the total weight of solvent and amine in the stream.

In the separator 32, MDI and MCB are separated, for example, by means of several distillation columns. The separated gaseous MCB is fed to a condenser 60 to make the separated MCB liquid. The liquid MCB can be split in a resource stream 62 to recover separated MCB, and a solvent purge 64, for example, to remove MCB so that impurities in the MCB are not increased. In the illustrated embodiment, the resource stream 62 is fed to a buffer tank 66 where the MCB can be stored for further use. Also, variations in the amount of the resource stream can be compensated for by way of the surge tank 66. The MCB recovered in the surge tank 66 can be fed to the recovery unit 52 for phosgene recovery and/or to the mixture stream 24 for MDA dissolution. Thus, resource stream 62 is an internal recycle stream in the isocyanate production process. The extract remaining from the recovered MCB is fed back to the reactor to enable further reaction of the remaining extract, preferably to form the desired product, such as MDI.

As illustrated in fig. 3, the MDI production process may be controlled by controlling the amount of solvent feed stream 54 and phosgene stream 16 based on the quantity and quality (concentration) of the at least one draw stream 38, 48. For this purpose, the flow rate (F) and the mass (Q) may be measured by the discharge flow measuring device 68 or calculated based on the concentration, temperature and level of the solution set 18 measured by the solution set measuring device 69. The flow rate and quality information of the exit streams 38, 48 are processed to set a solvent feed stream valve 70 for controlling the amount of solvent feed stream 54. The same information is used to set the phosgene stream valve 72 for controlling the amount of phosgene stream 16. The amount of phosgene stream 16 is set based on the amount of amine solution stream controlled by valve 82. The correction variables for setting the solvent feed stream valve 70 and the phosgene stream valve 72 are provided by a controller 74 for controlling the solvent feed stream 54 and the phosgene stream 16. To protect the stability of the MDI production process, the flow rate (F) of the solvent feed stream 54 is measured by the solvent feed stream measuring device 76. This allows the flow rate (i.e., the amount of phosgene stream 16) to be controlled by way of the phosgene stream valve 72 based on the flow rate or amount of the solvent feed stream 54 or even based on a target flow rate or target amount of the solvent feed stream 54. This control is provided by a controller 78 for controlling the phosgene stream 16.

Since the control of phosgene in the solution plant 18 is strongly related (coupled), multivariable controllers or similar structures have been designed for controlling the system. A drawback of conventional multivariable controllers is the realizability of the Distributed Control System (DCS). It is not very easy to design and install a conventional multivariable controller in a DCS. To avoid multivariable controllers, a different configuration using additional industry knowledge is preferred (fig. 4). In order to control the phosgene concentration in the solution installation 18, the amount of phosgene which interferes with the system can be calculated in a calculation device 86. The phosgene fed to the solvent unit 18 can be calculated from the phosgene amount of the phosgene stream 16 produced in the phosgene generation unit 14. It is sufficient for measuring the flow rate (amount) of the phosgene stream 16 by means of the phosgene stream measuring device 84. In the alternative, it is also possible to measure the concentration of phosgene in stream 20 by means of a measuring device 81. The amount of phosgene returned from reactor 22 can be calculated from the MDA loading and the excess of phosgene. The amount of MDA may be derived from a preset value of the mixture stream valve 82. This information, as well as other major fixed facts, is processed in the computing means 86 via the information input line 83. Of course, the dynamic behavior of these quantities of light must also be taken into account. The sum of the phosgene from the phosgene generation unit 14 and the recycle stream 50 can be included in the phosgene concentration control for control of the solvent feed stream valve 70 by the controller 74. The result is a simpler structure that operates as a multivariable controller and eliminates the need for a recycle stream measurement device 80 for measuring the flow rate (F) and concentration (Q) of the recycle stream 50.

Since too high an amount of phosgene and HCl in the phosgene purge 56 may jeopardize the neutralization/removal of phosgene and HCl, an overload control may be provided (fig. 5). A phosgene purge measurement device 88 is provided to measure the amount and/or quality of the phosgene purge 56. If it is found that the phosgene/HCl neutralization/removal can be compromised, the general control of the main controller 74 is overloaded until the hazard is eliminated. For this purpose, the solvent feed stream valve 70 is preferably opened.

In the embodiment of the invention illustrated in fig. 5, the recovery unit 52 and the solution unit 18 are grouped into a single absorption unit 28, the absorption unit 28 consisting of an absorption bed section 34 and an absorber bottom section 36. Since the phosgene recovery is performed in the absorption bed section 34, the absorption bed section 34 is also the recovery device 52. Since the dissolution of the phosgene produced in the MCB takes place in the absorber bottom 36, the absorber bottom 36 simultaneously also serves as the solution device 18. The recovery stream is located inside the absorber 28 between the absorber bed section 34 and the absorber bottom 36. It is thus possible to combine two different functions into one device. For example, if necessary, the solution unit 18 may be incorporated into the reactor 22, where the stream 20 is an internal stream of the reactor 22 consisting of several sub-units.

To prevent Cl in the phosgene stream 16₂The Cl in the phosgene stream 16 is measured by means of an additional phosgene stream measuring device 90 in the phosgene generation unit 14 (FIG. 6)₂And (5) monitoring. If Cl is found₂Then the photo gas stream valve 72 and/or the CO stream valve 92 and/or Cl are controlled by the controller 96₂The stream valve 94 is set to prevent Cl₂Into phosgene stream 16. The valves 72, 92, 94 are controlled by means of a controller 96 so that Cl is maintained₂A decrease in the amount of constituent phosgene stream 16 and/or an increase in phosgene production,this is by increasing the flow rate of the CO stream 10 and/or reducing the Cl₂Flow rate of the stream. Preferably, only the CO stream valve 92 is set by the controller 96. A further phosgene stream measuring device 90 makes it possible to determine the CO concentration in the phosgene stream 16 and thus to monitor the quality of the phosgene stream 16 in the usual manner by means of a further phosgene stream measuring device 90.

Since the pressure of the phosgene stream 16 influences the pressure of virtually all isocyanate production process units, the pressure of the phosgene stream 16 is monitored by means of a phosgene pressure measuring device 98 for controlling the pressure by means of the phosgene stream valve 72. To provide the desired phosgene flow rate, a CO feed measurement device 100 is provided in the CO stream 10, in Cl₂Providing Cl in stream 12₂A feed measurement device 102. The CO stream valve 92 and Cl are controlled by way of the CO feed measurement device 100 and Cl2 feed measurement device 102₂The stream valve 94 is provided to allow the phosgene generation unit 14 sufficient extract. Due to CO and Cl₂Are dependent on their pressure, thus providing a pre-pressure control. By CO pressure measurement device 104 and Cl₂Means for controlling the CO pressure valve 108 and Cl by means of the pressure measuring device 106₂A pressure valve 110. The measured pressures and flow rates are so strongly correlated with one another that adjusting one of the valves 72, 92, 94, 108 or 110 may cause a surge condition in the phosgene generation unit 14 and thus lead to instability in phosgene production. To avoid an unstable situation, the controllers for controlling the valves 72, 92, 94, 108, 110 include a time constant for adjusting the speed of each controller. Selection of an appropriate time constant provides a controller that can individually set its dedicated valve 72, 92, 94, 108, 110 faster or slower than the other controllers. The selection of a good time constant using general methods known to the person skilled in the art produces decoupling and thus facilitates control. For example, the CO pressure valve 108 and Cl₂The pressure valve 110 is set faster than the other valves 72, 92, 94, wherein the CO pressure valve 108 is adjusted to be Cl₂The pressure valve 110 is more rapid. Correspondingly, the CO stream is passed through a valve 92 and Cl₂The material flow valve 94 is provided withSet faster than phosgene stream valve 72, with CO stream valve 92 adjusted to ratio Cl₂The stream valve 94 is more rapid. This decoupling can be applied to other units or sub-units of the isocyanate production process.

Another possible control, for example, for the solution unit 18, the reactor 22, the separator 32, the isomer separation unit 42, the recovery unit 52, etc., or one of their sub-units, is illustrated by way of example in fig. 7. The means 112, which may be the solution means 18, the reactor 22, the separator 32, the isomer separation means 42, the recovery means 52, etc., are fed by a feed stream 114, which feed stream 114 is typically controlled by a feed valve 116. Typically, the flow rate, temperature, and pressure of the feed stream 114 are known or determined by a feed stream measurement device 118. Several process parameters of the device 112 are measured, such as concentration, temperature, level or pressure. To control the temperature, a temperature measuring device 120 is provided. The temperature of the device 112, as well as the flow rate and temperature of the feed stream 114, as measured by the temperature measuring device 120, are processed in the temperature controller 122. The temperature controller 122 takes into account the dynamic effect of the feed stream 114 on the temperature of the device 112, thereby enabling advanced temperature control. The temperature controller 122 controls a heating valve 124 through which a vapor stream 126 is regulated. Heating stream 126 is supplied to heat exchanger 128 where a portion of the liquid of apparatus 112 is heated. Cooling may be performed by using a cooling medium instead of steam. By way of temperature control, the concentration of the liquid in the device 112 can be controlled. If so, the information of the concentration is processed in the temperature controller 122 for calculating an optimal target temperature. The temperature control 122 further ensures that a given upper or lower temperature is not exceeded. The calculated target temperature is not higher than the upper limit temperature nor lower than the lower limit temperature.

Accordingly, the concentration of the component in the fluid is controlled. This concentration is determined by means of a concentration measuring device 130 and processed in a level controller 132 together with the flow rate information of the feed stream 114. The level controller 132 takes into account the dynamic effects of the feed stream 114 on the level and concentration of the device 112, thereby enabling advanced level and concentration control. The level controller 132 controls an output valve 134 through which the output flow rate of the output flow 136 is regulated. If a further output stream 138 is provided, this further output stream 138 can also be controlled in this way.

It is preferred to control the viscosity of the exit stream 38, especially when the exit stream 38 consists essentially of polymeric MDI. For this reason, a viscosity measuring device is provided to measure the viscosity of stream 38. This information is processed in a viscosity controller that controls, for example, the pressure and temperature of the separator 32.

The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings and other teachings in this specification are expressly contemplated. Those skilled in the art will recognize variations, modifications, and other implementations of what is described herein without departing from the spirit and scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and should not be construed in a limiting sense. The scope of the invention is defined in the following claims and equivalents thereof. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed. It is clear that the described embodiments can be used to form other materials, in particular other isocyanates, such as TDI, HDI, IPDI, starting from the corresponding amines such as TDA, HDA and using solvents such as MCB, ODB, etc.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (45)

1. A method of controlling a production process performed by a production facility comprising

a) At least two feed streams

b) At least one discharge stream

And

c) at least one internal recycle stream

The method comprises regulating the amount of at least one feed stream by means of a regulation control so as to control the concentration and/or amount of the output stream.

2. A method of controlling an isocyanate production process carried out by a production facility comprising

a) At least two feed streams comprising

(1) A phosgene stream containing phosgene, and

(2) a solvent stream comprising a solvent, wherein the solvent stream,

b) at least one discharge stream

And

c) at least one internal recycle stream

The method comprises controlling the concentration and/or amount of the discharge stream by adjusting the amount of the phosgene stream and/or the amount of the solvent stream in a regulated manner.

3. The method of claim 2, wherein the phosgene stream is fed to a solution unit, further comprising:

I. an amine solution stream comprising a mixture of an amine and a solvent is fed to a phosgene solution stream,

II. The combined stream is fed to a reactor,

III reacting the amines in the combined stream with phosgene in molar excess, based on the amino groups present, to form an isocyanate-containing product stream, which is fed from the reactor to a separator,

IV separation of the product stream in the separator into

(i) At least one isocyanate-containing discharge stream

And

(ii) at least one resource stream containing a solvent,

v, a stream comprising predominantly phosgene and/or HCl and a solvent stream are fed to the recycle stream of the recovery unit for the recovery of phosgene,

and

VI, feeding the recovery stream from the phosgene recovery unit to the solution unit.

4. The method of claim 3, wherein the solution unit, the reactor, the separator, the recovery unit, and the isomer distillation unit are controlled substantially independently of each other.

5. The method of claim 1, wherein the amount of the solvent stream is adjusted prior to and/or faster than the amount of the phosgene stream, and the adjustment is based on the amount of the amine feed stream.

6. The method of claim 1, wherein the amount of solvent feed stream is adjusted to be proportional to the amount of phosgene in the recycle stream and the amount of phosgene produced, the ratio being determined by a concentration controller for the phosgene solution; the amounts of phosgene produced and phosgene recirculated are calculated using the time and number change produced in the phosgene generation and the time change in the amount of phosgene stream, the time change in the amount and concentration of the mixture stream, and the reaction kinetics of the reactor, respectively.

7. The process of claim 1 wherein the amount of phosgene in the recycle stream and the concentration of solvent in the recycle stream are maintained by means of regulatory control of the recycle stream temperature and pressure.

8. The method of claim 3, wherein

(a) The first solution device control comprises:

(i) solvent concentration control in solution plants based on variation in the number of solvent feed streams

And

(ii) solution plant level control in relation to changes in phosgene stream quantities

And

(b) the second solution device control comprises

(i) Solvent concentration control in solution plants in relation to changes in the number of phosgene streams

And

(ii) solution plant level control associated with varying amounts of solvent feed stream,

the ratio at which the solution unit control, the target change in solvent concentration and the target level calculation are based depends on the frequency of the change in the number of solvent feed streams and/or the change in the number of phosgene streams, with the ratio controlled by the first solution unit being higher at lower frequencies.

9. The method of claim 3, wherein the amount of phosgene purged is controlled by the temperature of the recovery unit.

10. The method of claim 3, wherein the phosgene stream and the resource stream are adjusted after exceeding the first predetermined amount of purged phosgene until the amount of purged phosgene decreases below a second predetermined amount of purged phosgene.

11. The process of claim 2 wherein a CO stream comprising predominantly CO and comprising predominantly Cl are combined₂Cl of₂The stream is fed to a phosgene production unit which supplies a phosgene stream, the amount of phosgene stream and/or the amount of CO stream and/or Cl₂The amount of the stream is controlled independently of the target amount of phosgene used in the reactor.

12. A process according to claim 3, wherein level control is provided to at least a part of the recovery means and/or the reactor and/or the separator, the level control comprising standard level control and interference level control, wherein the interference level control is amplified more strongly relative to the standard level control.

13. The method of claim 12, wherein the level control is based on the interference level control when a first predetermined upper limit level is exceeded and/or a first predetermined lower limit level is below a target.

14. The method of claim 12, wherein the level control is based on a standard level control when a second predetermined upper level is below a target and/or exceeds a second predetermined lower level.

15. The process of claim 3, wherein the resource stream is fed to the solvent stream and/or the mixture stream via a buffer tank.

16. A process as claimed in claim 3, wherein the amine is present in the amine solution stream in an amount of from 15 to 95% by weight, based on the total weight of solvent and amine in the stream.

17. A process as claimed in claim 3, wherein the amine is present in the amine solution stream in an amount of from 15 to 85% by weight, based on the total weight of solvent and amine in the stream.

18. The process of claim 3 wherein phosgene is present in the phosgene solution stream in an amount of 15% by weight or more, based on the total weight of solvent and phosgene in the stream.

19. The process of claim 3 wherein phosgene is present in the phosgene solution stream in an amount of 20% by weight or more, based on the total weight of solvent and phosgene in the stream.

20. The process of claim 3 wherein phosgene is present in the phosgene solution stream in an amount of greater than or equal to 30% by weight, based on the total weight of solvent and phosgene in the stream.

21. The process of claim 3, wherein the weight ratio of solvent to amine in the combined stream is ≤ 10.

22. The process of claim 3 wherein the weight ratio of solvent to amine in the combined stream is 8 or less.

23. The process of claim 3, wherein the weight ratio of solvent to amine in the combined stream is ≥ 2 and ≤ 7.

24. A method of controlling an isocyanate production process in a production facility, the production facility comprising:

a) at least two feed streams comprising:

(1) a phosgene stream containing phosgene, and

(2) a solvent stream comprising a solvent, wherein the solvent stream,

b) at least one discharge stream

And

c) at least one internal recycle stream, and

the method comprises the following steps:

I. a phosgene stream is fed to the solution unit,

II. An amine solution stream comprising a mixture of an amine and a solvent is fed to a phosgene solution stream,

III feeding a stream of phosgene solution from the solution device into the reactor,

IV, reacting the amine solution stream with a phosgene solution stream to form an isocyanate-containing product stream, which is fed from the reactor to a separator,

v, separation of the product stream into

(i) At least one isocyanate-containing discharge stream

And

(ii) at least one resource stream containing a solvent,

VI, feeding a stream comprising predominantly phosgene and/or HCl and a solvent stream to the recycle stream of the recovery unit for the recovery of phosgene,

and

VII, feeding the recovery stream from the phosgene recovery device to a solution device,

wherein,

A. the solution unit, the reactor, the separator, the recovery unit and the isomer distillation unit are controlled substantially independently of each other,

B. the amount of the solvent stream is adjusted prior to and/or faster than the amount of the phosgene stream, which is based on the amount of the amine feed stream,

C. wherein the amount of solvent feed stream is adjusted in proportion to the amount of phosgene in the recycle stream and the amount of phosgene produced, said proportion being determined by the concentration controller for the phosgene solution; the amounts of phosgene produced and phosgene recirculated are calculated using the time and number change produced in the phosgene generation and the time change in the amount of phosgene stream, the time change in the amount and concentration of the mixture stream and the reaction kinetics of the reactor, respectively,

D. the solution control is carried out in the following manner

(a) A first solution device control comprising:

(i) solvent concentration control in solution plants based on variation in the number of solvent feed streams

And

(ii) solution plant level control in relation to changes in phosgene stream quantities

And

(b) a second solution unit control comprising

(i) Solvent concentration control in solution plants in relation to changes in the number of phosgene streams

And

(ii) solution plant level control associated with varying amounts of solvent feed stream,

wherein the ratio according to which the solution means control, the target change in solvent concentration and the target level calculation are based depends on the frequency of the change in the number of solvent feed streams and/or the change in the number of phosgene streams, at lower frequencies the ratio of the first solution means control is higher,

E. the amount of phosgene in the recycle stream and the concentration of solvent in the recycle stream are kept constant by means of the regulated control of the temperature and pressure of the recycle stream,

F. the amount of phosgene purged is controlled by the temperature of the recovery unit,

G. adjusting the phosgene stream and the resource stream after exceeding the first predetermined amount of purged phosgene until the amount of purged phosgene decreases below a second predetermined amount of purged phosgene,

H. a CO stream comprising mainly CO and comprising mainly Cl₂Cl of₂The stream is fed to a phosgene production unit which supplies a phosgene stream, the amount of phosgene stream and/or the amount of CO stream and/or Cl₂The amount of the stream is controlled independently of the target amount of phosgene used in the reactor,

I. providing level control to at least a part of the recovery means and/or the reactor and/or the separator, the level control comprising standard level control and disturbance level control, wherein the disturbance level control is amplified more strongly with respect to the standard level control,

J. when the first predetermined upper limit level is exceeded and/or the first predetermined lower limit level is below the target, the level control is based on the interference level control,

K. when the second predetermined upper limit level is lower than the target and/or exceeds the second predetermined lower limit level, the level control is based on the standard level control,

l, feeding the resource stream via a buffer tank into the solvent stream and/or the mixture stream,

m, the amine are present in the mixture stream in an amount of from 15 to 40% by weight, based on the total weight of the mixture stream.

25. The process of claim 24 wherein the amine is present in the amine solution stream in an amount of from 15 to 95 weight percent, based on the total weight of solvent and amine in the stream.

26. The process of claim 24 wherein the amine is present in the amine solution stream in an amount of from 15 to 85 weight percent, based on the total weight of solvent and amine in the stream.

27. The process of claim 24 wherein phosgene is present in the phosgene solution stream in an amount of 15 wt.% or more, based on the total weight of solvent and phosgene in the stream.

28. The process of claim 24 wherein phosgene is present in the phosgene solution stream in an amount of 20 wt.% or more, based on the total weight of solvent and phosgene in the stream.

29. The process of claim 24 wherein phosgene is present in the phosgene solution stream in an amount of greater than or equal to 30 weight percent based on the total weight of solvent and phosgene in the stream.

30. The process of claim 24 wherein the weight ratio of solvent to amine in the combined stream is ≤ 10.

31. The process of claim 24 wherein the weight ratio of solvent to amine in the combined stream is 8 or less.

32. The process of claim 24 wherein the weight ratio of solvent to amine in the combined stream is 2 or greater and 7 or less.

33. An isocyanate production facility comprising:

a) at least two feed streams comprising:

(1) a phosgene stream containing phosgene, and

(2) a solvent stream comprising a solvent, wherein the solvent stream,

b) at least one discharge stream

c) At least one internal recycle stream, the internal recycle stream,

and

d) a regulating control for regulating the amount of phosgene stream and/or the amount of solvent stream in order to control the concentration and/or quantity of the discharge stream.

34. The isocyanate production facility of claim 33, further comprising:

I. means for feeding a phosgene stream into the solution unit,

II. Means for feeding an amine solution stream comprising a mixture of an amine and a solvent into the phosgene solution stream,

III means for feeding a stream of phosgene solution from the solution device into the reactor,

IV reaction of the amine solution stream with the phosgene solution stream to form a reactor containing an isocyanate product stream, which is fed from the reactor

V, a separator for separating the product stream into

(i) At least one isocyanate-containing discharge stream

And

(ii) at least one resource stream containing a solvent,

VI, a stream comprising predominantly phosgene and/or HCl and a solvent stream are fed to the recycle stream of VII,

VII, a recovery device for recovering phosgene,

and

VIII, means for feeding the recovery stream from the phosgene recovery unit to the solution unit.

35. The facility of claim 34, wherein the solution unit, the reactor, the separator, the recovery unit, and the isomer distillation unit are controlled substantially independently of each other.

36. The facility of claim 33, wherein the adjustment to the amount of the solvent stream precedes and/or is faster than the adjustment to the amount of the phosgene stream.

37. The facility of claim 33, wherein the amount of solvent stream is varied based on the amount of phosgene produced, calculated using the variation in time and amount produced during phosgene generation.

38. The facility of claim 33, wherein

(a) The first solution device control comprises:

(i) solvent concentration control in solution plants based on variation in the number of solvent feed streams

And

(ii) solution plant level control in relation to changes in phosgene stream quantities

And

(b) the second solution device control comprises

(i) Solvent concentration control in solution plants in relation to changes in the number of phosgene streams

And

(ii) solution plant level control associated with varying amounts of solvent feed stream,

the ratio at which the solution unit control, the target change in solvent concentration and the target level calculation are based depends on the frequency of the change in the number of solvent feed streams and/or the change in the number of phosgene streams, with the ratio controlled by the first solution unit being higher at lower frequencies.

39. The facility of claim 33, wherein the amount of phosgene purged is controlled by the temperature of the recovery unit.

40. The facility of claim 33, wherein the phosgene stream and the resource stream are adjusted after exceeding the first predetermined amount of purged phosgene until the amount of purged phosgene decreases below a second predetermined amount of purged phosgene.

41. The facility of claim 33, wherein a CO stream comprising predominantly CO and a stream comprising predominantly Cl are combined₂Cl of₂The stream is fed to a phosgene production unit which supplies a phosgene stream, the amount of phosgene stream and/or the amount of CO stream and/or Cl₂The amount of the stream is controlled independently of the target amount of phosgene used in the reactor.

42. The facility of claim 33, wherein level control is provided to at least a portion of the recovery device and/or the reactor and/or the separator, the level control comprising standard level control and interference level control, wherein the interference level control is amplified more strongly relative to the standard level control.

43. The facility of claim 42, wherein the level control is based on the interference level control when a first predetermined upper limit level is exceeded and/or a first predetermined lower limit level is below a target.

44. The facility of claim 33, wherein the level control is based on a standard level control when a second predetermined upper level is below a target and/or exceeds a second predetermined lower level.

45. The facility of claim 34, wherein the resource stream is fed to the solvent stream and/or the mixture stream through a buffer tank.

Images