Method for controlling a reaction distillation column

Abstract

A method for controlling a reactive distillation column for carrying out a transalcoholization reaction is provided, comprising the steps of feeding a metal methoxide to the reactive distillation column via a side feed, feeding a reactant alcohol to a lower portion of the reactive distillation column, withdrawing methanol from the top of the reactive distillation column, and withdrawing a solution of the product metal alkoxide in the reactant alcohol from the bottom of the reactive distillation column, wherein the method includes a process control scheme selected from the following: Scheme A: establishing a signal S1 responsive to the temperature of a rectification section disposed above the metal methoxide feed inlet and manipulating the amount of reactant alcohol fed in response to signal S1, and Scheme B: establishing a signal S1 responsive to the temperature of a rectification section disposed above the metal methoxide feed inlet and manipulating the heat supplied to the bottom of the reactive distillation column in response to signal S1. The present invention also provides a method for controlling a reactive distillation column for conducting a transalcoholization reaction, comprising the steps of: supplying a metal methoxide to the reactive distillation column via a side feed, supplying a reactant alcohol to a lower portion of the reactive distillation column, presenting an auxiliary alcohol to the reactive distillation column, optionally supplementing the auxiliary alcohol via a side feed located above the reactant alcohol feed inlet and below the top of the distillation column, withdrawing methanol from the top of the reactive distillation column, and withdrawing a solution of the product metal alkoxide in the reactant alcohol from the bottom of the reactive distillation column, wherein the method includes a process control scheme selected from the following: Scheme C: establishing a signal S2 responsive to the temperature of a point located between the metal methoxide feed inlet and the bottom of the reactive distillation column and manipulating the reactant alcohol feed rate in response to signal S2; and Scheme D: establishing a signal S2 responsive to the temperature of a point located between the metal methoxide feed inlet and the bottom of the reactive distillation column and manipulating the heat supplied to the bottom of the reactive distillation column in response to signal S2. The method of the present invention allows for improved control of a reactive distillation column for carrying out a transalcoholization reaction.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a reaction distillation column for carrying out a transalcoholization reaction, which includes reacting a metal methoxide with a reactant alcohol to obtain a metal alkoxide as a product. [Background technology]

[0002] Metal alkoxides are useful as strong bases in the synthesis of numerous compounds, such as in the production of active ingredients for agricultural or pharmaceutical applications. Metal alkoxides can also be used as catalysts for base-catalyzed reactions, such as transesterification or amidation reactions, or as initiators for anionic polymerization.

[0003] Metal alkoxides can be converted to low-boiling alcohols (R) by reaction distillation, for example, as shown in the following formula. 1 OH) and metal alkoxides of high-boiling alcohols (MOR 2 To obtain a metal alkoxide of a low-boiling alcohol (MOR 1 ) and high-boiling point alcohols (R 2 It is obtained by trans-alcoholization with OH). [ka]

[0004] Such methods are described, for example, in German Patent Application Publication No. 27 26 491 and German Patent Application Publication No. 1 254 612. A mixture of a higher alcohol and a lower metal alkoxide is supplied to a reaction distillation column.

[0005] Desired high-boiling point alcohol metal alkoxide (MOR 2 The "product metal alkoxide" is generally withdrawn from the bottom of the column as a solution in a higher alcohol. At the top of the column, a low-boiling alcohol (R) is usually extracted. 1The OH(s) are extracted as a gas and condensed. A portion of the condensate is returned to the top of the column as reflux.

[0006] Metal methoxides are particularly suitable as starting materials for trans-alcoholization by reaction distillation because they are inexpensive and readily available. When using metal methoxides, methanol is produced as a low-boiling alcohol. To carry out reaction distillation economically, it is important to minimize the amount of methanol mixed into the product metal alkoxide in order to meet the desired specifications and avoid cost-intensive further processing.

[0007] However, controlling the reaction distillation column to achieve the required small amount of methanol in the product metal alkoxide has proven difficult. One approach is to adjust the purity of the product metal alkoxide solution by controlling the reflux ratio at the top of the column. The reflux ratio is the ratio of the amount of methanol condensate returned to the top of the column (reflux) to the amount of methanol condensate removed from the process. Generally, a higher reflux ratio results in a higher purity product metal alkoxide solution. However, a higher reflux ratio also increases the energy requirements of the process. Furthermore, adjusting the amount of condensate returned to the distillation column can cause variations in the amount of methanol in the product metal alkoxide solution.

[0008] U.S. Patent No. 4,377,443 describes a method for controlling a fractional distillation process in which a signal responds to the liquid level at the bottom of a fractional distillation column, and the flow rate of heat supplied to a heating fluid stream or an external flow is manipulated in response to the signal. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] German Patent Application Publication No. 2726491 [Patent Document 2] German Patent Application Publication No. 1254612 [Patent Document 3] U.S. Patent No. 4,377,443

Summary of the Invention

Problems to be Solved by the Invention

[0010] An object of the present invention is to provide a method for controlling a reactive distillation column for carrying out a transesterification reaction. It is desirable that this method does not exhibit the drawbacks of the methods known from the prior art as described above.

Means for Solving the Problems

[0011] In a first aspect, the present invention is a method for controlling a reactive distillation column for carrying out a transesterification reaction, comprising: - a step of supplying a metal methoxide to the reactive distillation column via a side feed; - a step of supplying a reactant alcohol to the lower part of the reactive distillation column; - a step of withdrawing methanol from the top of the reactive distillation column; - a step of withdrawing a solution of the product metal alkoxide in the reactant alcohol from the bottom of the reactive distillation column and providing a method including: This method is as follows: Scheme A: - establishing a signal S1 responsive to the temperature of the rectification section located above the feed port of the metal methoxide, and - a scheme for manipulating the feed rate of the reactant alcohol in response to the signal S1, and Scheme B: - establishing a signal S1 responsive to the temperature of the rectification section located above the feed port of the metal methoxide, and - a scheme for manipulating the heat supplied to the bottom of the reactive distillation column in response to the signal S1 including a process control scheme selected from:

[0012] Scheme A preferably includes further control schemes as follows. The amount of the withdrawn solution of the product metal alkoxide is manipulated according to the liquid level at the bottom of the distillation column. The heat supplied to the bottom of the reactive distillation column is manipulated according to the temperature at the bottom.

[0013] Scheme B preferably includes the following further control schemes: The amount of the extracted product metal alkoxide solution is controlled according to the liquid level at the bottom of the column. The amount of reactant alcohol supplied is controlled according to the temperature at the bottom of the distillation column.

[0014] In a second aspect, the present invention relates to a method for controlling a reaction distillation column for carrying out a trans-alcoholization reaction, - A step of supplying metal methoxide to the reaction distillation column via a side feed, - A step of supplying the reactant alcohol to the bottom of the reaction distillation column, - A step of introducing auxiliary alcohol into the reaction distillation column, and an optional step of replenishing auxiliary alcohol via a side feed located above the feed port for the reactant alcohol and below the top of the distillation column, - The process of removing methanol from the top of the reaction distillation column, - A step of removing the solution of the metal alkoxide product from the reactant alcohol at the bottom of the reaction distillation column. Includes, This method is as follows: Scheme C: - Establish a signal S2 that responds to the temperature of a point located between the metal methoxide feed port and the bottom of the reaction distillation column, and, - A scheme for controlling the supply amount of reagent alcohol in response to signal S2, and Scheme D: - Establish a signal S2 that responds to the temperature of a point located between the metal methoxide feed port and the bottom of the reaction distillation column, and, - A scheme to manipulate the heat supplied to the bottom of the reaction distillation column in response to signal S2. The present invention provides a method that includes a process control scheme selected from among them.

[0015] Scheme C preferably includes the following further control schemes: The amount of the extracted product metal alkoxide solution is controlled according to the liquid level at the bottom of the column. The heat supplied to the bottom of the reaction distillation column is controlled according to the temperature at the bottom of the column.

[0016] Scheme D preferably includes the following further control schemes: The amount of the extracted product metal alkoxide solution is controlled according to the liquid level at the bottom of the column. The supply of the reactant alcohol is controlled according to the temperature at the bottom of the distillation column.

[0017] A method according to a second embodiment is preferably as follows: Scheme E: - Establish a signal S3 that responds to the temperature of the rectification section located above the metal methoxide supply port, and, - A scheme to control the supply amount of auxiliary alcohol in response to signal S3. This includes further process control schemes. [Brief explanation of the drawing]

[0018] [Figure 1] The present invention illustrates a plant for the production of metal alkoxides, including a reaction distillation column for carrying out a trans-alcoholization reaction that can be controlled according to scheme A of a first aspect of the method of the present invention. [Figure 2] Further plants for producing metal alkoxides are shown, including a reaction distillation column for carrying out a trans-alcoholization reaction that can be controlled according to schemes C and E of a second aspect of the method of the present invention. [Figure 3A] The vertical temperature profile of the reaction distillation column in Example I-1 is shown. [Figure 3B] The vertical temperature profile of the reaction distillation column in Example I-2 is shown. [Figure 3C] The vertical temperature profile of the reaction distillation column in Example I-3 is shown. [Figure 3D] The vertical temperature profile of the reaction distillation column in Example I-4 is shown. [Figure 4] The vertical temperature profile of the reaction distillation column in Example II-1 is shown. [Modes for carrying out the invention]

[0019] The method according to the present invention is generally applicable to reactions between a metal methoxide and a reactant alcohol having a higher boiling point ("higher alcohol"), in which an optional auxiliary alcohol may be present, provided that the alcohol can be distilled at a dominant pressure in a reaction distillation column.

[0020] The metal methoxide and the reactant alcohol, or the metal methoxide, the reactant alcohol, and the auxiliary alcohol, are brought into contact in a reaction distillation column. In the context of this invention, the terms “reaction distillation column” and “distillation column” are used synonymously.

[0021] The reaction distillation column generally includes a reboiler, preferably a circulating reboiler. In the reboiler, a partial stream of the solution of the high-boiling point product metal alkoxide removed from the bottom of the column is heated and returned to the bottom of the column in at least partially gaseous form. Alternatively or additionally, the bottom of the column may be heated directly. A portion of the reactant alcohols remains in the reaction distillation column in gaseous form and rises toward the top of the column.

[0022] The reaction distillation column may be any commonly used reaction distillation column. Suitable types of reaction distillation columns include packed columns such as columns with random or structured packing, tray columns (i.e., tray columns), and mixed columns containing both packing and trays.

[0023] A suitable tray tower may have an internal structure over which the liquid phase flows. Suitable internal structures include sieve trays, bubble cap trays, valve trays, tunnel trays, and Thormann® trays, in particular bubble cap trays, valve trays, tunnel trays, and Thormann® trays.

[0024] Randomly packed columns may be packed with objects of various shapes. Heat and mass transfer is improved by increasing the surface area using molded bodies, typically ranging in size from 25 to 80 mm. Suitable shapes include Raschig rings (hollow cylinders), Lessing rings, Pall rings, Highflow rings, and Interox saddles. The packing material may be supplied to the distillation column in a regular or irregular manner (as bulk material, i.e., loosely packed). Suitable materials include glass, ceramics, metals, and plastics.

[0025] Structured packing is an evolution of regular packing, possessing a structure with a regular shape. This can reduce pressure loss in the gas flow. Suitable types of structured packing include cloth and metal sheet packing.

[0026] The term "top" or "head" of a distillation column refers to the area without internal structure located above the top tray or top packing. This is generally formed by a dome-shaped base (head, e.g., Klopper head or Korbbogen head) that forms the terminal element of the reaction distillation column.

[0027] The term "bottom" or "sump" in a distillation column refers to the area without internal structure located below the lowest tray or bottom packing.

[0028] A reaction distillation column generally includes a reboiler incorporated at the bottom of the column, or preferably a reboiler included in the sump circulation. The by-stream of the solution of the product metal alkoxide removed at the bottom of the column is supplied to the reboiler via the sump circulation and then returned to the distillation column as a heated fluid stream, which may optionally contain two phases. Suitable reboilers include evaporators, natural circulation reboilers, forced circulation reboilers, and forced circulation flash reboilers.

[0029] A forced-circulation reboiler uses a pump to circulate the liquid and evaporates it via a heater. The resulting gas-liquid mixture is then returned to the distillation column.

[0030] In a forced-circulation flash reboiler, a pump is also used to circulate the evaporating liquid through a heater. A superheated liquid is obtained, which is then reduced in pressure and sent to the bottom of the column. The pressure on the product metal alkoxide solution being recirculated into the distillation column increases due to the superheating. The superheated recirculated flow is reduced in pressure through a flow limiter. Thus, the liquid is superheated above its boiling point against the prevailing pressure in the distillation column.

[0031] When the superheated liquid passes through the flow limiter and re-enters the distillation column, rapid evaporation of the liquid occurs. This rapid evaporation results in a significant increase in volume and accelerates the fluid flow entering the distillation column. Preferably, the flow limiter is located immediately before the point where the superheated liquid re-enters the distillation column, or even inside the distillation column.

[0032] Preferably, the flow limiter is selected from orifice plates, valves, throttles, perforated discs, nozzles, capillaries, or a combination thereof. Preferably, a valve such as a rotary plug valve is used as the flow limiter. In a preferred embodiment, the opening profile of the flow limiter is adjustable. This makes it possible to maintain the pressure in the reboiler above the boiling pressure of the liquid relative to the dominant pressure in the distillation column under various flow velocities that may occur, for example, during the start and stop processes.

[0033] Advantageously, operating a reboiler as a forced-circulation or forced-flash circulation reboiler increases the fluid velocity within the heater, such as in the heat exchanger's tube bundle, compared to a natural circulation reboiler. Higher fluid velocity improves heat transfer between the heat exchanger and the heated fluid, preventing localized overheating.

[0034] Pumps used in forced-circulation evaporators or forced-circulation flash evaporators are preferably positioned between the removal line and the evaporator.

[0035] In a preferred embodiment, the distillation column is equipped with a forced-circulation evaporator, and the reactant alcohol is supplied in liquid form to a flow that is supplied to a forced-circulation reboiler.

[0036] Instead of, or in addition to, a bottom-circulating reboiler, the bottom of the column can be directly heated, for example, by an internal evaporator.

[0037] Ideally, the reactant alcohol ("trans-alcoholized alcohol") has a higher boiling point than methanol at the dominant pressure in the reaction distillation column. The term "product metal alkoxide" refers to a metal alkoxide containing the anion of the reactant alcohol. The term "auxiliary metal alkoxide" refers to a metal alkoxide containing the anion of the auxiliary alcohol.

[0038] In a distillation column, the gas phase and liquid phase are in countercurrent contact. Mass transfer occurs between the gas phase and the liquid phase. Highly volatile components accumulate in the gas phase towards the top of the column, while less volatile components accumulate in the liquid phase towards the bottom of the column.

[0039] The temperature-responsive signals, namely S1, S2, and S3, can each be established via any detection means, preferably a temperature sensor, suitable for determining the temperature inside the reaction distillation column.

[0040] The supply rate of the reactant alcohol can be controlled by an appropriate control element, such as a control valve. Similarly, the supply rate of the auxiliary alcohol can be controlled by an appropriate control element, such as a control valve.

[0041] The heat supplied to the bottom of the reaction distillation column can be manipulated, for example, by directly heating the bottom of the column, as described in more detail below, or by reboiler heating a partial stream of the product metal alkoxide solution removed from the bottom of the column.

[0042] The method according to the first embodiment involves the reaction of a metal methoxide with a reactant alcohol. At the bottom of the distillation column, the reactant alcohol is partially gaseous and rises toward the top of the column, while the solution of the metal methoxide drops toward the bottom of the column. The dropwise solution of the metal methoxide (MOCH3) is converted into a liquid reactant alcohol (R) as shown in the following formula. 1 It reacts with OH to produce a metal alkoxide (MOR 1 ) forms methanol. [ka]

[0043] In the trans-alcoholization reaction, methanol is withdrawn from the top of the reaction distillation column, and the solution of the product metal alkoxide in the reactant alcohol is withdrawn from the bottom of the column. In this way, an upper fraction and a bottom fraction are obtained. The purity of these fractions is critical to the efficiency of the trans-alcoholization reaction and the usefulness of the fractions.

[0044] Advantageously, the method of the present invention results in high purity for both the methanol obtained at the top of the column and the solution of the product metal alkoxide obtained at the bottom of the column. In other words, the resulting methanol contains only small or negligible amounts of the reactant alcohol, and the solution of the product metal alkoxide contains only small or negligible amounts of methanol and metal methoxide.

[0045] While we do not wish to be bound by theory, it is considered necessary to establish a vertical temperature profile of the distillation column that controls the heat input or the supply rate of the reactant alcohol at the bottom of the column to prevent methanol from flowing down to the bottom, in other words, to boil the reactant alcohol to the supply rate of metal methoxide or higher, in order to reduce the level of methanol contamination in the product metal alkoxide solution.

[0046] The method according to the first aspect of the present invention includes establishing a signal S1 that responds to the temperature of a rectification section disposed above the supply port of the metal methoxide. In one embodiment, the method includes establishing the signal S1 at the column height of the supply port of the metal methoxide or directly above the column height of the supply port of the metal methoxide.

[0047] In the first aspect, the heat supplied to the supply port of the reactant alcohol or the bottom of the reactive distillation column is operated in response to the signal S1.

[0048] The process control scheme of the present invention enables controlling the distillation column such that a stable temperature profile exists in the vertical direction of the distillation column. The temperature at the top of the column is close to the boiling point of methanol, indicating that the stream removed at the top is essentially pure methanol. At positions below the top of the column, the temperature increases. This is because the concentration of the reactant alcohol increases, indicating that the reactant alcohol boils at least up to the supply port of the metal methoxide.

[0049] Below the supply port of the metal methoxide, the temperature further increases due to the reaction of the reactant alcohol to the product metal alkoxide and the decrease in the concentration of methanol. Such a stable temperature profile can lower the methanol concentration in the solution of the product metal alkoxide.

[0050] In the first aspect, the reactant alcohol may be selected from linear, branched or cyclic monohydric C2-C 16 - alcohols such as ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tetradecanol, hexadecanol and their structural isomers (including cyclic alcohols and primary, secondary and tertiary forms of alcohols). In principle, polyhydric C2-C 10 - alcohols such as diols, for example ethylene glycol, diethylene glycol, propanediol or butanediol, and their structural isomers can also be used.

[0051] The carbon chain of the reactant alcohol may be interrupted by one or more oxygen atoms, with at least two carbon atoms present between the interrupting oxygen atoms and between the interrupting oxygen atoms and each hydroxyl group in the compound. Examples of monohydric alcohols in which the carbon chain is interrupted by oxygen atoms are 3-methyl-3-methoxybutanol or 1-methoxy-2-propanol.

[0052] The reactant alcohol may also contain one or more substituents that are inert under the conditions in the reaction distillation column, i.e., they do not react with the present compound or intermediate, such as -F or -Cl.

[0053] The reactant alcohol is preferably selected from ethanol, 2-propanol, 2-butanol, 3-methyl-2-butanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-methyl-3-hexanol, 3,7-dimethyl-3-octanol (tetrahydrolinalool, THL), 3,7-dimethyl-1-octanol, and 2,6-dimethyl-2-octanol (tetrahydromyrcenol). Ethanol and 3,7-dimethyl-3-octanol are particularly preferred.

[0054] The metal methoxide is preferably an alkali metal methoxide. More preferably, the metal methoxide is sodium methoxide or potassium methoxide, and most preferably sodium methoxide.

[0055] The metal methoxide is supplied to the reaction distillation column via a side feed. The term "side feed" means that the feed port is located below the top of the column but above the bottom. Preferably, the metal methoxide is supplied to the middle or upper half of the distillation column. The location of the metal methoxide feed port defines the rectification section (above the feed port) and the stripping section (below the feed port). Trans-alcoholization takes place in the stripping section of the distillation column.

[0056] Generally, metal methoxides are supplied to a distillation column as a solution, for example, via a pump. For example, metal methoxides may be supplied to a distillation column as a solution in methanol, the solution containing 20-40% by weight of metal methoxide, preferably 25-35% by weight of metal methoxide, for example 28-32% by weight of metal methoxide, based on the total weight of the metal methoxide solution. Percentages are given herein as weight percentages unless otherwise specified.

[0057] The feed inlet temperature for the metal methoxide solution is preferably at least 6°C, more preferably at least 10°C, and most preferably at least 20°C, for example, 25°C or 30°C. The metal methoxide solution can be preheated to its boiling point, for example, in a heat exchanger where the solution of the product metal alkoxide removed from the bottom of the column is simultaneously cooled. This is particularly advantageous with respect to the energy requirement of the trans-alcoholization reaction.

[0058] The reactant alcohol is supplied to one or more points below the metal methoxide feed inlet in the lower part of the reaction distillation column. The reactant alcohol may be supplied, for example, to the stripping section of the distillation column, the bottom of the column, and / or to a recirculation flow taken out from the bottom of the column. Preferably, the reactant alcohol is supplied to a recirculation flow taken out from the bottom of the column and / or the bottom. "Recirculation flow taken out from the bottom of the column" is understood to refer to a flow taken out from the bottom of the column and recirculated into the distillation column, preferably to the bottom of the column.

[0059] The reactant alcohol may be supplied to the distillation column in liquid or gaseous form. The reactant alcohol is preferably supplied to the bottom of the column and / or to the recirculation flow, particularly the recirculation flow, which is removed from the bottom of the column in liquid form.

[0060] At the top of the column, gaseous methanol is withdrawn. The withdrawn methanol is at least partially condensed, and a portion of the resulting condensate ("top condensate") is recycled back to the top of the column as reflux. The reflux ratio, i.e., the ratio of the amount of condensate returned to the distillation column (reflux) to the amount of condensate removed from the trans-alcoholization reaction, affects the purity of the product metal alkoxide solution withdrawn from the bottom of the column. It is preferable to maintain a constant reflux ratio during the trans-alcoholization reaction. This makes it possible to prevent fluctuations in the methanol content of the product metal alkoxide solution.

[0061] Condensation is preferably carried out in a plate heat exchanger, a shell-and-tube heat exchanger, or a straight-tube condenser, or several such condensers connected in series. It is preferable to use a straight-tube condenser, a shell-and-tube heat exchanger, or a combination thereof. Depending on the design, the condenser can be cooled by, for example, air, cooling water, or saltwater.

[0062] A portion of the condensate is recycled back to the top of the column as reflux, while the remainder is removed from the trans-alcoholization reaction. The reflux ratio affects the purity of the resulting gaseous fraction, particularly the liquid fraction. The reflux ratio is the ratio of the amount of condensate returned to the distillation column (kg / h) (reflux) to the amount of condensate removed from the trans-alcoholization reaction (kg / h).

[0063] The optimal reflux ratio primarily depends on the type of reactant alcohol used in the trans-alcoholization reaction and should be determined favorably by preliminary testing. The optimal reflux ratio can be determined by known methods such that it is economically optimal in terms of the energy required to separate methanol from the reactant alcohol, and that optimal conditions are achieved in terms of the purity of methanol removed from the trans-alcoholization reaction and the solution of the product metal alkoxide.

[0064] The methanol removed from the trans-alcoholization reaction, i.e., the condensate removed from the trans-alcoholization reaction, is generally of high purity and can be reused without further distillation. Preferably, only the excess amount of top condensate not required to adjust the reflux rate is removed from the system. The remaining top condensate is returned to the top of the column as reflux.

[0065] The top condensate can be used, for example, in the production of metal methoxides or solutions thereof.

[0066] The solution of the product metal alkoxide in the reactant alcohol is withdrawn from the bottom of the reaction distillation column. It is understood that the solution withdrawn from the "bottom of the reaction distillation column" includes the solution withdrawn from the recirculation flow taken from the bottom of the column, i.e., the solution withdrawn from the flow that is taken from the bottom of the column and recirculated back into the distillation column, preferably recirculated to the bottom of the column.

[0067] The solution of the product metal alkoxide removed from the bottom of the column, or removed from the recirculated flow withdrawn from the bottom of the column, generally consists essentially of the reactant alcohol and the product metal alkoxide. The withdrawn solution of product metal alkoxide typically contains 3 to 90% by weight of the product metal alkoxide relative to the total weight of the withdrawn solution. The amount of product metal alkoxide in the withdrawn solution generally depends on the solubility of the product metal alkoxide in the reactant alcohol. Some product metal alkoxides are liquid at STP (20°C and 1 bar absolute pressure). For example, sodium tetrahydrolinalolate is liquid at STP. Improved liquid stability allows for more reliable avoidance of product metal alkoxide precipitation over the length of the reaction distillation column. Additionally, the product metal alkoxide can be withdrawn as a highly concentrated solution.

[0068] For efficiency, the trans-alcoholization reaction should be carried out such that the extracted solution of the product metal alkoxide contains as much of the product metal alkoxide as possible. The concentration of the product metal alkoxide in the solution can be determined, for example, by titration. The concentration of the product metal alkoxide in the solution is influenced by the volume ratio of the metal methoxide supply to the reactant alcohol supply.

[0069] The solution of the product metal alkoxide can optionally be cooled in a heat exchanger and then used as is. Alternatively, the product metal alkoxide may be isolated from the solution in the reactant alcohol by, for example, evaporation of the reactant alcohol, according to methods known in the art.

[0070] In the process according to the first embodiment, it is preferable that the rectification section of the distillation column is provided with a tray, and the stripping section of the distillation column is provided with a tray or packing material. In the second embodiment, it is preferable that both the rectification section and the stripping section of the distillation column include a tray.

[0071] The number of theoretical plates in the rectification section is determined by the difference in vapor pressure between the reactant alcohol and methanol; therefore, a larger number of theoretical plates is advantageous when the difference is small. The number of theoretical plates in the stripping section is determined by the difference in vapor pressure between the reactant alcohol and methanol, as well as the equilibrium position of the trans-alcoholization reaction. When the equilibrium is mainly on the side of the starting materials, a larger number of theoretical plates is advantageous. The number of theoretical plates in both the rectification and stripping sections also depends on the desired purity of the products at the bottom and top of the column, and the reflux ratio used; therefore, a larger number of theoretical plates is required to achieve higher purity at a given reflux ratio.

[0072] Reaction distillation columns can operate under ambient pressure as well as under reduced or high pressure. The dominant pressure in a distillation column is preferably an absolute pressure in the range of 0.2 to 10 bar, more preferably an absolute pressure in the range of 0.5 to 3 bar, and most preferably an absolute pressure of 0.7 to 1 bar.

[0073] The equilibrium position of trans-alcoholization may be temperature-dependent for some alkoxides. In these cases, higher temperatures can result in higher turnover. Operating the distillation column under high pressure, for example, at an absolute pressure of at least 1.5 bar, at least 2.5 bar, or at least 5.0 bar, may also be advantageous.

[0074] In a reaction distillation column, the reaction equilibrium is constantly readjusted due to continuous mass transfer and changes in concentration in the gas and liquid phases, enabling a high conversion rate. When starting the distillation column, methanol can be supplied to the top of the column to adjust the reflux rate, and the stripping section and sump can be filled with the reactant alcohol. Methanol can also be added to the reactant alcohol.

[0075] After reaching the operating temperature, a solution of metal methoxide is added. Fresh methanol is continuously formed during the reaction.

[0076] In some cases, this process involves the reactant alcohol, particularly C. 10- In the production of metal alkoxides from high-boiling point alcohols such as alcohols, a problem arises due to the low solubility of metal methoxides. Because of this limited solubility, metal methoxides often result in undesirable precipitates in the distillation column. Such precipitates are more likely to occur when there is a large difference in the number of carbon atoms between the reactant alcohol and methanol. These solid deposits can clog the distillation column, and their removal requires interrupting the reaction distillation and emptying the column, which is a time-consuming and costly process. It has been found that this problem can be avoided or mitigated by introducing an auxiliary alcohol into the distillation column.

[0077] Therefore, in a second embodiment, an auxiliary alcohol is present in the reaction distillation column to improve or at least mitigate the problem of solubility limitations. The boiling point of the auxiliary alcohol is between the boiling point of methanol and the boiling point of the reactant alcohol at the dominant pressure in the reaction distillation column.

[0078] The reactant alcohol and auxiliary alcohol at the bottom of the reaction distillation column are partially gaseous and rise towards the top of the column, while the solution of metal methoxide drops down towards the bottom of the column. As shown in the following formula, the dropping solution of metal methoxide (MOCH3) is a liquid auxiliary alcohol (R X It reacts with OH) to form methanol and the auxiliary metal alkoxide (MOR X ) forms. [ka]

[0079] Gaseous methanol rises towards the top of the column, while the solution of the auxiliary metal alkoxide drips down towards the bottom of the column. As shown in the following equation, the auxiliary metal alkoxide (MOR X The dropwise solution of ) contains the liquid reagent alcohol (R 1 It reacts with OH to produce a metal alkoxide (MOR 1 ) and auxiliary alcohol (R X It forms an OH group. [ka]

[0080] The solubility of metal methoxide in auxiliary alcohols is generally higher than that in reactant alcohols; therefore, auxiliary alcohols make metal methoxide and reactant alcohols compatible. Consequently, the formation of solid deposits in the distillation column is significantly reduced or completely prevented. In particular, auxiliary alcohols are not consumed in the alcohol exchange reaction and essentially remain in the reaction distillation column. Nevertheless, due to the inevitable loss of auxiliary alcohols, it is necessary to continuously add fresh auxiliary alcohols to the distillation column.

[0081] Advantageously, the method of the present invention results in high purity for both the methanol obtained at the top of the column and the solution of the product metal alkoxide obtained at the bottom of the column. In other words, the obtained methanol contains only small or negligible amounts of auxiliary alcohols and reagent alcohols, and the solution of the product metal alkoxide contains only small or negligible amounts of methanol, metal methoxide, auxiliary alcohols, and auxiliary metal alkoxides.

[0082] In the method according to the second embodiment, an auxiliary alcohol is present in the reaction distillation column. The auxiliary alcohol is not consumed and essentially remains in the reaction distillation column. Nevertheless, in order to maintain an effective concentration of the auxiliary alcohol in the distillation column over a long period of production, it may be necessary to replenish the column with auxiliary alcohol in a batch or continuous manner, preferably in a continuous manner.

[0083] The process control scheme of the present invention makes it possible to control the distillation column so that a stable temperature profile exists in the longitudinal direction of the distillation column.

[0084] The temperature at the top of the column is close to the boiling point of methanol, indicating that the flow removed at the top is essentially pure methanol. In the region directly below the top of the column, the temperature rises. This is due to the increasing concentration of the auxiliary alcohol, which boils at least up to the metal methoxide feed port.

[0085] Below the supply port for the metal methoxide, there is a further temperature increase due to the reaction of the auxiliary alcohol with the auxiliary metal alkoxide and the decrease in methanol concentration.

[0086] Further down, there is another temperature rise due to the reaction of the auxiliary metal alkoxide with the reactant alcohol and the decrease in the concentration of the auxiliary alcohol. This temperature rise is located roughly midway between the metal methoxide feed port and the reactant alcohol feed port. If the temperature rise is too close to the metal methoxide feed port, there will be insufficient reaction space for the reaction between the metal methoxide and the auxiliary alcohol. If the temperature rise is too close to the reactant alcohol feed port, there will not be enough space for the reaction between the auxiliary metal alkoxide and the reactant alcohol, and the solution of the product metal alkoxide withdrawn from the bottom of the column will contain a relatively high concentration of auxiliary alcohol, and possibly methanol.

[0087] Such a stable temperature profile allows for lower concentrations of auxiliary alcohols and methanol in the solution of the resulting metal alkoxide.

[0088] In a second embodiment, the method includes establishing a signal S2 that responds to the temperature of a point located longitudinally between the feed port of the metal methoxide and the bottom of the reaction distillation column. Preferably, the signal S2 is established at approximately equidistant longitudinal points between the feed port of the metal methoxide and the bottom of the column.

[0089] In actual embodiments, the distillation column is a tray column. In this embodiment, ratio n up :n down However, a signal S2 is established that responds to the temperature on the signal establishment tray, with a ratio of 1.5:1 to 1:1.5, preferably 1.2:1 to 1:1.2. Here, n up n is the number of trays on the signal establishment tray up to the metal methoxide supply port. down This is the number of trays below the signal-establishing tray at the bottom of the tower.

[0090] Unless otherwise specified, the descriptions of embodiments and preferred embodiments of the first embodiment are also applicable to the second embodiment of the present invention.

[0091] Auxiliary alcohols can be supplied via a side feed located below the top of the column, above the feed port for the reactant alcohol. Preferably, the auxiliary alcohols are supplied via a longitudinal side feed between the feed port for the metal methoxide and the feed port for the reactant alcohol, or together with the metal methoxide. More preferably, the auxiliary alcohols are supplied to the distillation column via a longitudinal side feed between the feed port for the metal methoxide and the feed port for the reactant alcohol. It is particularly preferable that the auxiliary alcohols be supplied to the distillation column via a side feed immediately below the feed port for the metal methoxide.

[0092] It is also possible to supply auxiliary alcohol to the reaction distillation column above the metal methoxide feed port. In this case, the distillation column must have sufficient trays or internal packing material above the auxiliary alcohol feed port to provide a sufficient number of separation stages to separate methanol from the auxiliary alcohol.

[0093] The auxiliary alcohol is preferably supplied to a reaction distillation column that is well above the bottom of the column. In actual embodiments, the side feed of the auxiliary alcohol is located at least 5 trays longitudinally from the bottom of the column. For example, in a distillation column with 80 trays, the metal methoxide can be supplied to the 40th tray, the auxiliary alcohol to the 38th tray, and the reactant alcohol to the 10th tray.

[0094] In the second embodiment, the heat supplied to the feed port of the reactant alcohol or to the bottom of the reaction distillation column is controlled in response to the signal S2.

[0095] In a second embodiment, the method preferably includes a further process control scheme, which involves establishing a temperature-responsive signal S3 in a rectification section located above the metal methoxide feed port. In one embodiment, the method includes establishing the signal S3 at the height of the metal methoxide feed port or directly above the height of the metal methoxide feed port.

[0096] In this embodiment, the amount of auxiliary alcohol supplied is controlled according to the signal S3.

[0097] In the second embodiment, the reactant alcohol is a monovalent C6-C 16 - Alcohols may be selected. In principle, polyvalent C2-C such as diols, e.g., ethylene glycol, diethylene glycol, propanediol or butanediol, and their structural isomers. 10 -Alcohol can also be used.

[0098] In a second embodiment, the reactant alcohol is preferably particularly selected from 3-methyl-3-methoxybutanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-methyl-3-hexanol, 3,7-dimethyl-3-octanol (tetrahydrolinalool, THL), 3,7-dimethyl-1-octanol, and 2,6-dimethyl-2-octanol (tetrahydromyrcenol). 3,7-dimethyl-3-octanol is particularly preferred.

[0099] The auxiliary alcohol preferably has a boiling point at least 10°C, more preferably at least 15°C, and most preferably at least 20°C higher than the boiling point of methanol at the dominant pressure in the reaction distillation column. Preferably, the boiling point of the auxiliary alcohol is at least 10°C, more preferably at least 15°C, and most preferably at least 20°C lower than the boiling point of the reactant alcohol at the dominant pressure in the reaction distillation column.

[0100] The auxiliary alcohol can be selected from monohydric C3-C7 alcohols, namely propanol, butanol, pentanol, hexanol, heptanol, and their structural isomers, such as cyclic alcohols, as well as primary, secondary, and tertiary forms of alcohols. The carbon chain of the alcohol may be interrupted by one or more oxygen atoms, with at least two carbon atoms present between the interrupting oxygen atoms and between the interrupting oxygen atoms and each hydroxyl group in the compound. An example of a monohydric alcohol in which the carbon chain is interrupted by oxygen atoms is 1-methoxy-2-propanol.

[0101] The auxiliary alcohol may also contain one or more substituents that are inert under the conditions of the reaction distillation column, i.e., they do not react with the present compound or intermediate, such as -F or -Cl.

[0102] Suitable auxiliary alcohols include 1-methoxy-2-propanol, 2-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, tert-butanol, 3-methyl-3-pentanol, and 3-ethyl-3-pentanol. 2-butanol, 1-methoxy-2-propanol, and 3-methyl-2-butanol, particularly 3-methyl-2-butanol, are especially preferred.

[0103] In a second aspect of the present invention, the number of theoretical plates in the rectification section is determined by the difference in vapor pressure between the auxiliary alcohol and methanol; therefore, a larger number of theoretical plates is advantageous when the difference is small. The number of theoretical plates in the stripping section is determined by the difference in vapor pressure between the auxiliary alcohol and the reactant alcohol, as well as the equilibrium position of the trans-alcoholization reaction. A larger number of theoretical plates is advantageous when the equilibrium is mainly on the side of the starting material. The number of theoretical plates in both the rectification and stripping sections also depends on the desired purity of the bottom and top products and the reflux ratio used; therefore, a larger number of theoretical plates is required to achieve higher purity at a given reflux ratio.

[0104] To start the reaction distillation column, fill it with auxiliary alcohol and reactant alcohol, using the auxiliary alcohol as reflux initially. After reaching the operating temperature, add the metal methoxide solution. This allows the system to be controlled in a steady state, enabling a smooth transition to continuous reaction distillation with the addition of metal methoxide. Starting the addition of metal methoxide involves maintaining a constant temperature in the distillation column, especially at the bottom, until the final operating temperature is reached.

[0105] In particular, the method of the present invention relates to the range of possible combinations of metal alkoxides and alcohols, for example, in one particular embodiment, the alcohol may constitute a reactant alcohol, and in another particular embodiment, it may constitute an auxiliary alcohol. In a second aspect of the present invention, it is understood that the specific examples of metal methoxides, reactant alcohols and auxiliary alcohols provided above are illustrative and do not limit the possibilities of the alcohol constituting either an auxiliary alcohol or a reactant alcohol, for example, depending on the differences in the boiling points of the components used in a particular embodiment.

[0106] The present invention will be further illustrated by the accompanying drawings and the following embodiments.

[0107] Figure 1 shows a plant for the production of metal alkoxides, including a reaction distillation column for carrying out a controllable trans-alcoholization reaction according to scheme A of a first embodiment of the method of the present invention. The plant shown in Figure 1 includes a reaction distillation column 101. A solution of metal methoxide is supplied to the distillation column 101 via line 102. The reactant alcohol is supplied to the bottom of the distillation column 101 via line 103, a reboiler 110, and line 111. At the top of the distillation column 101, gaseous methanol is withdrawn via line 104 and condensed in condenser 105. The first stream of condensed methanol is removed from the trans-alcoholization reaction via line 106, and the second stream of condensed methanol is returned to the top of the distillation column 101 via line 107. The solution of the product metal alkoxide in the reactant alcohol is withdrawn from the bottom of the column. The first stream of the product metal alkoxide solution is removed from the trans-alcoholization reaction via line 108, and the second stream of the product metal alkoxide solution is returned to the bottom of the column via line 111, together with the reactant alcohol from line 103, via line 109 and reboiler 110. In the rectification section located above the supply port 102, a signal S1 is established via the temperature sensor TIC1, and the supply amount of the reactant alcohol is controlled via the control valve 112 in response to the signal S1.

[0108] Figure 2 shows a further plant for producing metal alkoxides, including a reaction distillation column for carrying out a trans-alcoholization reaction that can be controlled according to schemes C and E of a second embodiment of the method of the present invention. The plant shown in Figure 2 includes a reaction distillation column 201. A solution of metal methoxide is supplied to the distillation column 201 via line 202. Auxiliary alcohol is supplied to the distillation column 201 via line 203. Reactant alcohol is supplied to the distillation column 201 via line 204. At the top of the distillation column 201, gaseous methanol is withdrawn via line 205 and condensed in condenser 206. The first stream of condensed methanol is removed from the trans-alcoholization reaction via line 207, and the second stream of condensed methanol is returned to the top of the distillation column 201 via line 208. The solution of the product metal alkoxide in the reactant alcohol is withdrawn from the bottom of the column. The first stream of the product metal alkoxide solution is removed from the trans-alcoholization reaction via line 209, and the second stream of the product metal alkoxide solution is returned to the bottom of the column via line 210, reboiler 211, and line 212. Below the location of the supply port 203, a signal S2 is established via the temperature sensor TIC2, and the supply amount of the reactant alcohol is controlled via the control valve 214 in response to the signal S2. In the rectification section located above the supply port 202, a signal S3 is established via the temperature sensor TIC3, and the supply amount of auxiliary alcohol is controlled via the control valve 213 in response to the signal S3.

[0109] Figure 3A shows the vertical temperature profile of the reaction distillation column in Example I-1. Figure 3B shows the vertical temperature profile of the reaction distillation column in Example I-2. Figure 3C shows the vertical temperature profile of the reaction distillation column in Example I-3. Figure 3D shows the vertical temperature profile of the reaction distillation column in Example I-4. Figure 4 shows the vertical temperature profile of the reaction distillation column in Example II-1. [Examples]

[0110] Examples I-1 to I-4 Examples I-1 to I-4 were carried out according to the first embodiment of the present invention, i.e., in the absence of auxiliary alcohol.

[0111] IA. Determination of reagent alcohols in the top condensate of the column. A sample of the top condensate was taken, 1,4-dioxane was added as an internal standard, and the sample was analyzed for its reactant alcohol content by gas chromatography (separation column RTX-5 amine, length 30 m, inner diameter 0.32 mm, film thickness 1.5 μm, TCD detector). The detection limit was approximately 500 mg / kg.

[0112] IB. Determination of methanol in bottom output. IB.1 Reagent: Alcohol: Isopropanol or 2-butanol When isopropanol was used as the reagent alcohol, 150 mg of the sample solution of the product metal alkoxide was weighed into a headspace vial (22.5 mL). When 2-butanol was used as the reagent alcohol, 60 mg of the sample solution of the product metal alkoxide was weighed into a headspace vial (22.5 mL).

[0113] The sample was mixed with 1 mL of tap water, sealed with an aluminum cap, and analyzed by headspace GC (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 μm). Quantitative analysis was performed using the standard addition method. The detection limit was less than 100 mg / kg.

[0114] In the standard addition method, multiple measurements of the sample are performed, for example, duplicate measurements. A specific amount of the substance to be measured (reactant alcohol) is added to each sample several times, and the sample is measured after each addition. The increase in the amount of substance is measured. The concentration of the reactant alcohol in the original sample can be calculated by linear regression.

[0115] The solubility of the sample must be confirmed beforehand. If two phases are formed, the weight of the sample needs to be reduced.

[0116] IB.2 Reagent: Alcohol ::2-methyl-2-butanol A 500 mg sample of the metal alkoxide solution was taken and cooled to room temperature (approximately 23°C). The sample was mixed with approximately 1 mL of water and 0.5 mg of tert-butanol (as an internal standard) in 1 mL of dioxane, one drop of phosphoric acid was added, and the sample was diluted by adding 3 mL of dioxane (without an internal standard). If the sample was solid, it was melted at 60°C and then mixed with water, tert-butanol, phosphoric acid, and dioxane.

[0117] Diluted samples were analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 μm). Quantitative analysis was performed using the standard addition method. The detection limit was 200 mg / kg.

[0118] IB.3 Reagent: Alcohol: 3-methyl-3-pentanol A 500 mg sample of the product metal alkoxide solution was taken and cooled to room temperature (approximately 23°C). The sample was mixed with approximately 1 mL of water and 0.5 mg of hexane (as an internal standard) in 1 mL of dioxane, one drop of phosphoric acid was added, and then diluted with 3 mL of dioxane (without an internal standard) to obtain the sample. If the sample was solid, it was melted at 60°C and then mixed with water, hexane, phosphoric acid, and dioxane.

[0119] Diluted samples were analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 μm). Quantitative analysis was performed using the standard addition method. The detection limit was 200 mg / kg.

[0120] Determination of product metal alkoxides in IC bottom output. To determine the amount of metal alkoxide product at the bottom of the column, samples were taken, and the total base content, consisting of alkoxide, hydroxide, and carbonate, was determined by titration with trifluoromethanesulfonic acid (0.1 mol / l in 2-propanol) in 2-propanol. The amounts of hydroxide and carbonate were determined by volumetric Karl Fischer titration (KFT), as these components react with the KF component in KFT to form water. The alkoxide content was determined by subtracting the contributions of hydroxide and carbonate from the total base content.

[0121] ID. Examples I-1 to I-4 The examples were carried out in a plant that basically followed Figure 1, including a reaction distillation column with 80 glass bubble cap trays and a forced-circulation flash reboiler. In Examples I-1 to I-3, the reactant alcohol was supplied to the recirculation flow entering the reboiler. In Example I-4, the reactant alcohol was supplied from the bottom of the column to the 10th tray. Table 1 shows the specific parameters of the examples.

[0122] The reboiler was heated with a commercially available thermostat (Julabo HT6) with a maximum heating power of 5700 W. The diameter of the distillation column was 50 mm. To avoid heat loss, the distillation column was isothermally heated with an electrically protected heating system.

[0123] Before starting, the distillation column was filled with the reactant alcohol. Once the operating temperature was reached, sodium methoxide and the reactant alcohol were supplied to the distillation column.

[0124] Sodium methoxide (30% by weight in methanol) was supplied to the distillation column by side feed.

[0125] The amounts of product metal alkoxide and methanol ("bottom output") in the solution of the product metal alkoxide removed at the bottom of the column were determined.

[0126] At the top of the column, gaseous methanol was removed and condensed in a condenser. The amounts of reagent alcohol and auxiliary alcohol in the top condensate were measured.

[0127] In the rectification section located above the sodium methoxide supply port, specifically on tray 62, a signal S1 is established via temperature sensor TIC1, and the supply amount of reactant alcohol is controlled via a control valve in response to signal S1.

[0128] Figures 3A to 3D show the vertical temperature profiles of the reaction distillation column for Examples I-1 to I-4. As is clear from Figures 3A to 3D, the process control scheme of the present invention allows the distillation column to be controlled so that a stable temperature profile exists in the vertical direction of the column. In all of Figures 3A to 3D, the temperature rises in the region below the top of the column. Below the metal methoxide feed port, there is a further temperature increase.

[0129] [Table 1]

[0130] Example II-1 Example II-1 was carried out according to the second embodiment of the present invention, that is, in the presence of an auxiliary alcohol. Specifically, tetrahydrolinalool was used as the reactant alcohol and 3-methyl-2-butanol was used as the auxiliary alcohol.

[0131] IIA. Determination of tetrahydrolinalool and 3-methyl-2-butanol in the top condensate. Samples of the top condensate were taken, 1,4-dioxane was added as an internal standard, and the samples were analyzed for their THL and 3-methyl-2-butanol content by gas chromatography (separation column RTX-5 amine, length 30 m, inner diameter 0.32 mm, film thickness 1.5 μm, TCD detector). The detection limit was approximately 500 mg / kg.

[0132] IIB. Determination of methanol and 3-methyl-2-butanol in bottom output. A 500 mg sample of the product metal alkoxide solution was taken and cooled to room temperature (approximately 23°C). The sample was mixed with 0.5 mg of n-hexane (as an internal standard) in 1 mL of isopropanol, one drop of phosphoric acid was added, and then diluted with 3 mL of isopropanol (without an internal standard) to obtain the sample. If the sample was solid, it was melted at 60°C and then mixed with hexane, phosphoric acid, and ethanol.

[0133] Diluted samples were analyzed by gas chromatography (separation column DB-1, length 30 m, inner diameter 0.25 mm, film thickness 1.0 μm). Quantitative analysis was performed using the standard addition method. The detection limit was 200 mg / kg. In the standard addition method, multiple measurements of the sample are performed, e.g., duplicate measurements. A specific amount of the substance to be measured (reactant alcohol) is added to each sample several times, and the sample is measured after each addition. The increase in the amount of substance is measured. The concentration of the reactant alcohol in the original sample can be calculated by linear regression.

[0134] The solubility of the sample must be confirmed beforehand. If two phases are formed, the weight of the sample needs to be reduced.

[0135] IIC. Determination of sodium alkoxide tetrahydrolinalate in bottom output. To determine the amount of sodium alkoxide tetrahydrolinalolate at the bottom of the column, samples were taken, and the total content of bases consisting of alkoxides, hydroxides, and carbonates was determined by titration with trifluoromethanesulfonic acid (0.1 mol / l in 2-propanol) in 2-propanol. The amounts of hydroxides and carbonates were determined by volumetric Karl Fischer titration (KFT) because these components react with the KF component in KFT to form water. The alkoxide content was determined by subtracting the contributions of hydroxides and carbonates from the total base content.

[0136] IID. Example II-1 Example II-1 was carried out in a plant that basically followed Figure 2, including a reaction distillation column with 80 glass bubble cap trays and a forced-circulation flash reboiler. Tetrahydrolinalool (THL) was supplied to the recirculation flow entering the reboiler. Table 2 shows the specific parameters of Example II-1.

[0137] The reboiler was heated with a commercially available thermostat (Julabo HT6) with a maximum heating power of 5700 W. The diameter of the distillation column was 50 mm. To avoid heat loss, the distillation column was isothermally heated with an electrically protected heating system.

[0138] Before starting, the distillation column was filled with auxiliary alcohol and reactant alcohol. Once the operating temperature was reached, sodium methoxide and reactant alcohol were supplied to the distillation column. Sodium methoxide (30% by weight in methanol) was supplied to the distillation column by side feed.

[0139] The amounts of the product metal alkoxide, auxiliary alcohol, and methanol ("bottom output") in the solution of the product metal alkoxide removed at the bottom of the column were determined. At the top of the column, gaseous methanol was removed and condensed in a condenser. The amounts of the reactant alcohol and auxiliary alcohol in the top condensate were measured.

[0140] In tray 20, signal S2 was established via temperature sensor TIC2, and the supply amount of THL was controlled via control valve in response to signal S2. In tray 72, signal S3 was established via temperature sensor TIC3, and the supply amount of auxiliary alcohol was controlled via control valve 213 in response to signal S3.

[0141] Figure 4 shows the longitudinal temperature profile of the reaction distillation column for example, II-1. As is clear from Figure 4, the process control scheme of the present invention allows the distillation column to be controlled so that a stable temperature profile exists longitudinally. In Figure 4, the temperature rises in the region just below the top of the column. Below the metal methoxide feed port, there is a further temperature increase. Further down, there is another temperature increase.

[0142] [Table 2] [Explanation of symbols]

[0143] 101 Reaction distillation column Line 102 Line 103 Line 104 105 Capacitor Line 106 Line 107 108 Line Line 109 110 Reboiler Line 111 112 Control valve 201 Reaction distillation column Line 202 Line 203 Line 204 205 Line 206 Capacitors Line 207 208 Line Line 209 210 lines 211 Reboiler 212 lines 213 Control valve 214 Control valve

Claims

1. A method for controlling a reaction distillation column to carry out a trans-alcoholization reaction, - A step of supplying metal methoxide to the reaction distillation column via a side feed, - A step of supplying a reactant alcohol to the lower part of the reaction distillation column, wherein the lower part includes a stripping section below the supply position of the metal methoxide, a bottom and / or a recirculating flow taken out from the bottom of the column, - A step of extracting methanol from the top of the reaction distillation column, - A step of removing the solution of the product metal alkoxide in the reactant alcohol from the bottom of the reaction distillation column. - Steps to establish a vertical temperature profile of the distillation column by boiling the reactant alcohol to the metal methoxide feed port or higher. Includes, The aforementioned method is as follows: Scheme A: - Establish a signal S1 that responds to the temperature of the rectification section located above the supply port of the metal methoxide, and, - A scheme for controlling the supply amount of the reagent alcohol in response to the signal S1; and Scheme B: - Establish a signal S1 that responds to the temperature of the rectification section located above the supply port of the metal methoxide, and, - A scheme for manipulating the heat supplied to the bottom of the reaction distillation column in response to the signal S1. A method including a process control scheme selected from.

2. The method according to claim 1, wherein the reactant alcohol is selected from ethanol, 2-propanol, 2-butanol, 3-methyl-2-butanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-methyl-3-hexanol, and 3,7-dimethyl-3-octanol.

3. A method for controlling a reaction distillation column to carry out a trans-alcoholization reaction, - A step of supplying metal methoxide to the reaction distillation column via a side feed, - A step of supplying a reactant alcohol to the lower part of the reaction distillation column, wherein the lower part includes a stripping section below the supply position of the metal methoxide, a bottom and / or a recirculating flow taken out from the bottom of the column, - A step of introducing auxiliary alcohol into the reaction distillation column, and an optional step of replenishing the auxiliary alcohol via a side feed located above the supply port for the reactant alcohol and below the top of the reaction distillation column, - A step of extracting methanol from the top of the reaction distillation column, - A step of removing the solution of the product metal alkoxide in the reactant alcohol from the bottom of the reaction distillation column. Includes, The aforementioned method is as follows: Scheme C: - Establish a signal S2 that responds to the temperature of a point located between the feed port of the metal methoxide and the bottom of the reaction distillation column, and, - A scheme for controlling the supply amount of the reagent alcohol in response to the signal S2; and Scheme D: - Establish a signal S2 that responds to the temperature of a point located between the feed port of the metal methoxide and the bottom of the reaction distillation column, and, - A scheme for manipulating the heat supplied to the bottom of the reaction distillation column in response to the signal S2. A method including a process control scheme selected from.

4. The method described above is Scheme E: - Establish a signal S3 that responds to the temperature of the rectification section located above the supply port of the metal methoxide, and, - A scheme for controlling the supply amount of the auxiliary alcohol in response to the signal S3. The method according to claim 3, further comprising a process control scheme.

5. The method according to claim 3 or 4, wherein the reactant alcohol is selected from 3-methyl-3-methoxybutanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-methyl-3-hexanol, and 3,7-dimethyl-3-octanol.

6. The method according to any one of claims 3 to 5, wherein the dominant pressure in the distillation column is an absolute pressure in the range of 0.2 to 10 bar, and the boiling point of the auxiliary alcohol is at least 10°C higher than the boiling point of methanol at the dominant pressure in the reaction distillation column.

7. The method according to any one of claims 3 to 6, wherein the dominant pressure in the distillation column is an absolute pressure in the range of 0.2 to 10 bar, and the boiling point of the auxiliary alcohol is at least 10°C lower than the boiling point of the reactant alcohol at the dominant pressure in the reaction distillation column.

8. The method according to any one of claims 3 to 7, wherein the auxiliary alcohol is selected from 1-methoxy-2-propanol, 2-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, tert-butanol, 3-methyl-3-pentanol, and 3-ethyl-3-pentanol.

9. The method according to any one of claims 1 to 8, wherein the metal methoxide is an alkali metal methoxide.

10. The method according to claim 9, wherein the alkali metal methoxide is sodium methoxide or potassium methoxide.

11. The method according to any one of claims 1 to 10, wherein the metal methoxide is supplied to the reaction distillation column as a solution in methanol, and the solution contains 20 to 40% by weight of the metal methoxide relative to the total weight of the solution of the metal methoxide.

12. The method according to any one of claims 1 to 11, wherein the reaction distillation column comprises a forced-circulation reboiler, and the reactant alcohol is supplied in liquid form to the flow supplied to the forced-circulation reboiler.

13. The method according to any one of claims 1 to 12, wherein the product metal alkoxide is a liquid at a temperature of 20°C and an absolute pressure of 1 bar.

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