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Reaction control method and control apparatusRelated Patent Categories: Chemical Apparatus And Process Disinfecting, Deodorizing, Preserving, Or Sterilizing, Chemical Reactor, Including Heat Exchanger For Reaction Chamber Or Reactants Located ThereinReaction control method and control apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060093535, Reaction control method and control apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a Divisional of co-pending application Ser. No. 10/257,320 filed on Oct. 10, 2002 and for which priority is claimed under 35 U.S.C. .sctn. 120. Application Ser. No. 10/257,320 is the national phase of PCT International Application No. PCT/JP02/01333 filed on Feb. 15, 2002 under 35 U.S.C. .sctn. 371. The entire contents of each of the above-identified applications are hereby incorporated by reference. TECHNICAL FIELD [0002] This invention relates to a reaction control method (or stabilization method) and a reaction control apparatus that are useful for stabilizing a reaction system for a carbonylation reaction, etc. BACKGROUND ART [0003] Carboxylic acids (such as acetic acid, etc.) and derivatives thereof (such as methyl methacrylate, etc.) are produced industrially by use of carbonylation reactions. For example, Japanese Patent Application Laid-open No. 54011/1973 (JP-48-54011A) discloses a carbonylation method in which an olefin, an alcohol or ester thereof, a halide, or ether derivative is allowed to react in the liquid phase with carbon monoxide in the presence of a catalytic system containing a rhodium or iridium component and an iodine or bromine component. In this process, at least part of the liquid reactants is passed without heating through a separation zone that is substantially low in pressure to vaporize at least part of an above-mentioned carbonylation product, the vaporized carbonylation product is taken out, and the residual liquid reactants are recirculated to the above-mentioned reaction zone. With this literature, the removal of unreacted carbon monoxide from the reactor is indicated. Japanese Patent Application Laid-open No. 321847/1994 (JP-6-321847A) indicates a carbonylation product recovery method in which an iridium catalyst is used as the carbonylation catalyst, a vapor component containing the carbonylation product and a liquid component containing the iridium catalyst are generated by vaporization of the reaction product, the vapor component and the liquid component are separated, and the concentration of water in the liquid component is maintained at least at 0.5 weight %. With this literature, the discharge of unreacted carbon monoxide as exhaust gas from the reactor is illustrated. [0004] Japanese Patent Application Laid-open No. 508594/1998 (JP-10-508594A) proposes a method comprising a first region, in which a carboxylic acid is produced by liquid phase carbonylation in the presence of a rhodium catalyst, and a second region, in which the reaction mixture is partially vaporized, and wherein a vapor fraction containing the produced carboxylic acid is refined and the non-vaporized liquid fraction containing the catalyst is circulated to the first region, carbon monoxide is added to the non-vaporized liquid fraction generated from the second region with preventing return of carbon monoxide to the second region to avoid loss of carbon monoxide. [0005] However with such carbonylation reactions, the temperature and pressure of the reaction system fluctuate or vary with the circulation of the high boiling point component to the reaction system, causing the carbon monoxide consumption rate or usage rate of the reaction system to fluctuate and thus making the stabilization of the reaction system difficult. Also, the carbon monoxide discharge rate increases in accompaniment with the supplying of excess carbon monoxide and fluctuation of the carbon monoxide consumption rate of the reaction system. Carbon monoxide therefore could not be used effectively in the carbonylation reaction. [0006] Japanese Patent Application Laid-open No. 95723/2000 (JP-2000-95723A) discloses a control method for a process of producing acetic acid by carbonylation, wherein the flow of carbon monoxide that passes through a control valve is measured, the average value of the carbon monoxide flow within a predetermined term is calculated, a fixed value is added to this average carbon monoxide flow to calculate the maximum flow rate of carbon monoxide, and operation is performed so that the flow rate of carbon monoxide into the reactor will not exceed the maximum flow rate. With this method, since the carbon monoxide flow rate is controlled using a maximum flow rate, determined by adding a fixed value to the average carbon monoxide flow, as a reference, it is difficult to suppress fluctuations of the temperature and pressure of the reaction system and thereby stabilize the reaction system. [0007] Thus an object of the present invention is to provide a reaction control method (or stabilization method) and a reaction control apparatus (or stabilization apparatus) by which a liquid phase reaction system, such as a carbonylation reaction system, can be stabilized effectively. [0008] Another object of the present invention is to provide a reaction control method (or stabilization method) and a reaction control apparatus (or stabilization apparatus) with which the temperature and pressure fluctuations of a liquid phase reaction system are controlled to enable stable production of products in an industrially advantageous manner. DISCLOSURE OF INVENTION [0009] The inventors of the present invention made intensive studies to achieve the above objects, and finally found that (1) even when a separated component (such as a high boiling point component or fraction, etc.), which has been separated by distillation from a carbonylation reaction mixture, is circulated (or returned) to the reaction system (i.e., the pressurized reaction system) steadily at a predetermined rate, the circulation rate (return flow rate) of the separated component will fluctuate, the temperature of the reaction system will fluctuate accordingly, the pressure of the reaction system will fluctuate in accompaniment with this temperature change even when carbon monoxide is supplied to the reaction system steadily at a predetermined rate, and the above-mentioned temperature and pressure fluctuations will be large especially in the case where the reaction temperature of an exothermic reaction system is controlled by the circulation rate (return flow rate) of the separated component and without using a cooling unit, and that (2) when the temperature of the circulated separated component is controlled according to (or depending on) the heat quantity of the separated component that is returned to the reaction system, the temperature and pressure fluctuations of the reaction system can be suppressed (or restrained) effectively, the discharge amount of carbon monoxide can be reduced to enable effective use of carbon monoxide for reaction, and the reaction system can be stabilized. The present invention was accomplished based on the above finding. [0010] That is, the reaction control method (or stabilization method) of this invention is a method in which, while supplying reaction components continuously into a liquid-phase reaction system (e.g., a pressurized liquid-phase reaction system), part of the reaction product in the reaction system is subjected continuously to a separation step and the separated component (a high boiling point component or fraction, etc., that has been separated from a low boiling point component or fraction) that has been separated in the separation step is circulated (or returned) to the above-mentioned reaction system, wherein the temperature of the above-mentioned reaction system is controlled by controlling the heat quantity of the separated component that is circulated or returned to the reaction system in association with the circulation rate (return flow rate) of the separated component from the above-mentioned separation step. With this method, the separated component that is circulated or returned to the reaction system usually contains effective or useful components (catalytic components, etc.) that are effective for the reaction. The method of this invention can be applied favorably to a system, wherein the circulation rate (return flow rate) of a separated component (a circulated component such as a high boiling point) from the separation step to the reaction system fluctuates. With such a system, it is useful, for control of the reaction system temperature at a predetermined temperature, to detect the flow rate and temperature of the circulated separated component (the circulated component such as the high boiling point component) and to control the temperature of the circulated separated component (or circulated component) based on the detected flow rate and temperature. Though the reactor may be equipped with a heat removal unit or a cooling unit, this invention is preferably applied to an exothermic reaction system that the reactor is not equipped with a heat removal unit or cooling unit and the temperature of this exothermic reaction system (or reactor) can be controlled by the temperature and flow rate of a separated component that is lower in temperature than the reaction system (or reactor). In the present invention, usually, treatments or operations in the above-described steps may be conducted continuously or successively. [0011] The above-described reaction control method (reaction stabilization method) can be utilized in various liquid phase reaction systems, such as carbonylation reaction systems (a pressurized carbonylation system). For example, the method can be applied to a system, wherein an alcohol and carbon monoxide are supplied into a liquid phase reaction system that comprises a carbonylation catalytic system, part of the reaction mixture comprising the carboxylic acid produced by the reaction is drawn out from the reaction system while maintaining a substantially constant liquid level of the reaction system and is subjected to a flash distillation, and a high boiling point component or fraction is circulated or returned to the reaction system, the high boiling point component comprises the carbonylation catalytic system and is separated by the flash distillation from a low boiling point component or fraction comprising the carbonylation product. The high boiling point component may contain a carbonylation catalytic system comprising a rhodium catalyst and a cocatalyst, and the low boiling point component may contain a carboxylic acid, a carboxylic acid ester and an alkane halide. With this system, the low boiling point component that has been separated by the flash distillation may be further subjected to a refining system for separating into a second low boiling point component or fraction, a component containing a carboxylic acid, and a second high boiling point component or fraction, and the second low boiling point component that has been separated by this refining system may be circulated or returned to the reaction system. With this carbonylation reaction, the second low boiling point component usually contains a cocatalyst (e.g., an alkane halide), etc. The above-mentioned liquid phase reaction system may be a reaction system in which methanol and carbon monoxide are reacted in the presence of a carbonylation catalytic system to produce acetic acid or a derivative thereof. By such a method, the reaction temperature can be controlled at extremely high precision and pressure fluctuations of the liquid phase reaction system can be suppressed (or restrained) significantly as well. For example, the temperature of the reaction system can be controlled within a range of .+-.0.5.degree. C. with respect to a reference temperature. The reference temperature may be 150 to 220.degree. C. [0012] The control apparatus (stabilization apparatus) of this invention is equipped with the above-described liquid phase reaction system, a separation unit such as a distillation column, a temperature control unit for controlling the temperature of the separated component that has been separated by the separation unit, and a circulation line for circulating or returning the separated component that has been adjusted in temperature by the temperature control unit to the reaction system. This apparatus is also equipped with a flow rate sensor (or flow sensor) for detecting the circulation rate (return flow rate) of the separated component in the above-mentioned circulation line, a temperature sensor for detecting the temperature of the separated component in the above-mentioned circulation line, and a control unit, by means of the temperature control unit and based on the detection data from the flow rate sensor and temperature sensor, for controlling the heat quantity of the separated component that is circulated or returned to the reaction system. With the above-described apparatus, separation into a low boiling point component and a high boiling point component is carried out by the separation unit, and the high boiling point component is circulated or returned via the circulation line (first circulation line) to the reaction system. The separated low boiling point component can then be separated by a refining unit into a second low boiling point component, a component containing a carboxylic acid, and a second high boiling point component, and the second low boiling point component may be circulated or returned to the reaction system via a second circulation line. The above-described liquid phase reaction system may be practically a liquid phase exothermic reaction system without (that is not equipped with) a cooling unit, and the control unit may serve as a unit that controls the heat quantity of the separated component that is lower in temperature than the reaction system by means of the temperature control unit and controls the reaction temperature by the circulation rate (return flow rate) of the circulated separated component. [0013] With the present specification, the expression "maintaining a substantially constant liquid level of the reaction system" means that the liquid level (the height level of the liquid surface) is maintained substantially constant on the average. That is, this expression shall not be limited to the case where the liquid level is maintained statically at a constant level, and it is sufficient for the liquid level to be substantially constant on the average even in the case where the liquid level fluctuates due to sparging of a gaseous component, etc. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 shows a process flow diagram for explaining a reaction control method and control apparatus of this invention, and [0015] FIG. 2 is a block diagram for explaining the control apparatus of FIG. 1. BEST MODE FOR CARRYING OUT THE INVENTION [0016] The present invention shall now be described in detail with reference as necessary to the attached drawings. FIG. 1 is a process flow diagram for explaining a control method and control apparatus of this invention. FIG. 2 is a block diagram for explaining the control apparatus of FIG. 1. [0017] This embodiment illustrates a process for producing a carboxylic acid (such as acetic acid, etc.) by a carbonylation reaction of an alcohol (such as methanol, etc.) and carbon monoxide in the presence of a carbonylation catalytic system comprising a rhodium catalyst, lithium iodide, and methyl iodide. [0018] This process is equipped with a compressor 1 for pressurizing the carbon monoxide as the gaseous reaction component (reactant), a feed line 17 for supplying or feeding the pressurized carbon monoxide continuously at a predetermined rate to a reactor 3 via a buffer tank 2, a feed line 19 for supplying the alcohol (methanol, etc.) as the liquid reaction component (reactant) continuously at a predetermined rate to the reactor 3, and a feed line 20 for continuously drawing out from the reactor part of the reaction mixture, which contains the carbonylation product (a carboxylic acid, such as acetic acid or a derivative thereof) produced by the reaction, with maintaining a substantially constant liquid level of the reactor 3, to supply the drawn the reaction mixture (the draw stream) to a flash distillation column 4, which serves as the separation unit. The reactor 3 comprises a liquid phase reaction system that includes the carbonylation catalytic system (a catalytic system comprising a principal or main catalytic component, such as rhodium catalyst, etc., and cocatalysts, such as lithium iodide and methyl iodide, etc.), and the carbon monoxide, which is the gaseous reactant, is sparged from the lower part or bottom of the reactor 3. Such a liquid phase reaction system (or reactor) is an exothermic reaction system (or reactor) accompanying with exothermic reaction. The above-described reactor 3 may be equipped with a heat removal unit or a cooling unit for controlling the reaction temperature, while is preferably not equipped with a heat removal unit or a cooling unit. [0019] The gaseous component from the reactor 3 contains unreacted carbon monoxide, methyl iodide as the cocatalyst, byproduct methane, etc. This gaseous component containing such components is supplied from the above-described reactor 3 to an absorption system for recovery of the cocatalyst, such as methyl iodide, etc., and the recovered cocatalyst can then be reused in the reaction. Continue reading about Reaction control method and control apparatus... Full patent description for Reaction control method and control apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Reaction control method and control apparatus patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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