Method and apparatus for producing acrylic acid by lactate dehydration reaction

Abstract

This invention relates to a method for producing acrylic acid by a lactate dehydration reaction and an apparatus for producing the same.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2023-0048056 dated April 12, 2023, and all content disclosed in the documents of said Korean Patent Application is incorporated herein by reference.

[0002] This invention relates to a method for producing acrylic acid by a lactate dehydration reaction and an apparatus for producing the same. [Background technology]

[0003] Acrylic acid is used as a polymer raw material in fibers, adhesives, paints, textile processing, leather, and building materials, and its demand is expanding. Furthermore, acrylic acid is also used as a raw material for superabsorbent resins and is widely used industrially in absorbent products such as disposable diapers and sanitary napkins, water-retaining agents for agriculture and horticulture, and industrial water-stopping materials. Conventional methods for producing acrylic acid generally involve the air oxidation of propylene. This method involves converting propylene to acrolein through a gas-phase catalytic oxidation reaction, and then producing acrylic acid through a gas-phase catalytic oxidation reaction of acrolein. However, acetic acid is produced as a byproduct, which is difficult to separate from acrylic acid. Furthermore, the aforementioned propylene-based acrylic acid production method uses propylene obtained by refining crude oil, a fossil resource, as a raw material. Considering the recent rise in crude oil prices and issues such as global warming, this method presents problems in terms of raw material costs and environmental pollution.

[0004] In response to this, research has been conducted on methods for producing acrylic acid from carbon-neutral biomass raw materials. For example, there is a method for producing acrylic acid (AA) by the gas-phase dehydration reaction of lactic acid (LA). This method generally produces acrylic acid by the intramolecular dehydration reaction of lactic acid at high temperatures of 300°C or higher and in the presence of a catalyst.

[0005] However, during the production of acrylic acid by lactic acid dehydration, lactic acid has a high boiling point, which leads to the formation of oligomers. This can result in inaccurate measurements of lactic acid content using conventional methods, or prolonged analysis times. Additionally, the by-product propanoic acid generates coke on the catalyst surface, reducing the catalyst's lifespan. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the present invention provides a method for producing acrylic acid by a lactate dehydration reaction that allows for easy control of the reaction process by analyzing the reaction products of the lactate dehydration reaction within a short time. [Means for solving the problem]

[0007] Therefore, the present invention provides a step (Step 1) of producing a reaction product containing acrylic acid by a lactate dehydration reaction in the presence of a catalyst; Step 2: Condensing the reaction product to produce a liquid mixture; Step 3: Continuously pass the liquid mixture through an optical cell and analyze the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the liquid mixture in real time using a near-infrared spectrometer; and Step 4 includes a step (determining one or more of the reaction temperature and catalyst regeneration in Step 1 based on the analysis results in Step 3, This invention provides a method for producing acrylic acid by a lactate dehydration reaction.

[0008] Furthermore, the present invention relates to a reaction section in which a lactate dehydration reaction is carried out in the presence of a catalyst; The present invention provides a lactic acid dehydration reaction apparatus comprising: a discharge section for discharging reaction products; an absorption tower or condenser connected to the discharge section for condensing the reaction products to produce a liquid mixture; a supply section for continuously supplying the liquid mixture from the bottom of the absorption tower or condenser to the optical cell of a near-infrared spectrometer; a near-infrared spectrometer for real-time analysis of the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the supplied liquid mixture; and a near-infrared analysis signal processing and control device.

[0009] In the present invention, terms such as "first," "second," etc., are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from other components.

[0010] Furthermore, the terms used herein are used solely to illustrate exemplary embodiments and are not intended to limit the invention.

[0011] A singular expression includes plural expressions unless the context clearly indicates otherwise.

[0012] In this specification, terms such as “includes,” “equip,” or “have” are used to describe the features, figures, steps, components, or combinations thereof that have been implemented, and do not preclude one or more other features, figures, steps, components, combinations thereof, or additions.

[0013] Furthermore, where it is referred to in this specification that each layer or element is formed "on top of" each layer or element, it means either that each layer or element is formed directly on top of each layer or element, or that other layers or elements may be formed additionally between each layer, on the object, or on the substrate.

[0014] The present invention can be modified in various ways and may take many forms; therefore, specific embodiments are illustrated and described in detail below. However, this should not be understood as limiting the present invention to any particular form of disclosure, but rather as including any modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0015] In this specification, lactic acid may include lactic acid isomers, and lactic acid derivatives are used as a concept that encompasses both naturally occurring lactic acid dimers and lactic acid oligomers.

[0016] The present invention will be explained in more detail below to help you understand it better.

[0017] The present invention provides a method for producing acrylic acid by a lactic acid dehydration reaction, comprising the steps of: producing a reaction product containing acrylic acid by a lactic acid dehydration reaction in the presence of a catalyst (Step 1); condensing the reaction product to produce a liquid mixture (Step 2); passing the liquid mixture continuously through an optical cell and analyzing the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the liquid mixture in real time using a near-infrared spectrometer (Step 3); and determining the production temperature of the reaction product and / or the regeneration of the catalyst based on the analysis results of Step 3 (Step 4).

[0018] Furthermore, the method for producing acrylic acid by the lactic acid dehydration reaction described above can be realized using the following apparatus.

[0019] For example, a lactate dehydration reaction apparatus is provided, comprising: a reaction section in which a lactate dehydration reaction is carried out in the presence of a catalyst; a discharge section for discharging the reaction product; an absorption tower or condenser connected to the discharge section for condensing the reaction product to produce a liquid mixture; a supply section for continuously supplying the liquid mixture from the bottom of the absorption tower or condenser to the optical cell of a near-infrared spectrometer; a near-infrared spectrometer for real-time analysis of the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the supplied liquid mixture; and a near-infrared analysis signal processing and control device.

[0020] Lactic acid is widely used in the production of acrylic acid. When producing acrylic acid by dehydrating lactic acid, since it is carried out by a gas-phase reaction, it is necessary to vaporize lactic acid into lactic acid molecules. At this time, due to the high boiling point of lactic acid and the high reaction temperature, oligomers are formed. Generally, when using gas chromatography to analyze the product, the content of lactic acid in the reaction product tends to be underestimated. When using liquid chromatography, since the separation of the reaction product must be carried out first, there is a problem that the analysis of the product content is somewhat delayed.

[0021] As described above, if the content of each component in the reaction product is mismeasured or the content analysis is delayed, it may cause a decrease in the reaction activity of the catalyst due to the formation of coke on the catalyst surface, etc., and problems may occur in the reaction process. This may result in affecting the yield of the target acrylic acid and causing problems in the economy of the entire process.

[0022] Therefore, the inventors of the present invention condensed the reaction product to produce a liquid mixture, passed this through an optical cell, and used a near-infrared spectrometer to analyze the concentrations of lactic acid, a lactic acid derivative containing lactic acid oligomers, acrylic acid, and propanoic acid, which are the main products in the liquid mixture, in real time during the reaction, and by quickly and accurately determining the reactor temperature and / or the regeneration time point of the catalyst in the reactor, found that the above problems can be prevented, and thus completed the present invention.

[0023] Hereinafter, each step will be specifically described.

[0024] (Step 1) In the method for producing acrylic acid by lactic acid dehydration reaction of the present invention, Step 1 is a step of producing a reaction product containing acrylic acid by lactic acid dehydration reaction in the presence of a catalyst.

[0025] The reaction for producing acrylic acid by dehydration within the lactic acid molecule can be carried out as follows and is generally known to be carried out in the presence of a catalyst. [ka]

[0026] To produce acrylic acid by dehydration of lactic acid, the process may generally include a step of vaporizing lactic acid to obtain lactic acid molecules, and the details of the lactic acid vaporization can be those of reactors and / or reaction conditions that are generally known in the art to which the present invention belongs.

[0027] The method for producing acrylic acid from vaporized lactic acid can also be applied to catalysts, reactors, and / or reaction conditions that are generally known in the art to which the present invention pertains.

[0028] Furthermore, dehydration reactions using solid catalysts may be carried out as continuous reactions using fixed reactors or as batch reactions. When using fixed reactors, the reactor is filled with solid catalysts, and the reactants are continuously supplied to the reactor to carry out the reaction, thereby allowing for the continuous production of the product.

[0029] Furthermore, during the lactic acid dehydration reaction, lactic acid may be supplied in aqueous solution form, in which case the concentration of the aqueous lactic acid solution may be 10% by weight or more, 20% by weight or more, or 30% by weight or more, and 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less.

[0030] The temperature of the dehydration reaction may be approximately 300°C to 500°C, or approximately 320°C to 400°C. The reaction pressure may be approximately 1 atmosphere to 5 atmospheres, or approximately 1 atmosphere to 2 atmospheres.

[0031] The rate of reaction supply may vary depending on the shape and type of reactor, other reaction conditions, etc. Specifically, for example, it may be carried out so that the weight hourly space velocity (WHSV) of lactic acid supplied over gas is approximately 0.05 to approximately 1.0 / hr, or approximately 0.10 to approximately 0.50 / hr.

[0032] If the conditions described above are not met, a decomposition reaction by hydrogenation may occur, potentially leading to problems such as reduced reaction efficiency or a lower conversion rate.

[0033] In step 1 of the present invention, the reaction product produced by the lactate dehydration reaction includes acrylic acid and may also include unreacted lactic acid, lactic acid oligomers, and propanoic acid produced by side reactions. On the other hand, the lactic acid oligomer refers to a substance in which lactic acid reacts with each other to form dimers, trimers, etc., or refers to a form in which water molecules are removed and dehydration condensation occurs.

[0034] (Step 2) Step 2 of the present invention is the step of condensing the reaction product produced in Step 1 to produce a liquid mixture. The reaction product discharged from the reactor is generally in the form of a gaseous mixture under superheated conditions. Therefore, it is desirable to produce it as a liquid mixture for the transfer and storage of the reaction product.

[0035] The liquid mixture in step 2 can be supplied using an absorption tower or condenser, as described later, and the configuration of the absorption tower or condenser can be one of the apparatus and / or conditions commonly known in the art to which the present invention belongs.

[0036] On the other hand, the production of the liquid mixture in step 2 may be carried out under temperature conditions of 50°C to 250°C. If carried out at a temperature exceeding 250°C, the gas-phase reaction product may not be able to be liquefied, and the amount lost may increase. If carried out at a temperature below 50°C, excessive energy consumption may become a problem. Preferably, it may be carried out at a temperature of 60°C or higher, 70°C or higher, or 80°C or higher, and 220°C or lower, 200°C or lower, or 180°C or lower.

[0037] According to one aspect of the present invention, step 2 can be used to produce a liquid mixture of gaseous products using water. The method by which water is used in the absorption tower or condenser is not particularly limited, but water may be injected by providing injection nozzles at the top or one or more positions of the absorption tower or condenser to facilitate contact with the reaction products. The direction in which the water is injected may be parallel to the flow direction of the reaction products, axially, or against the flow direction, or any combination thereof.

[0038] In step 2 of the present invention, the method for producing a liquid mixture can use the condenser or absorption tower described above, and the condenser or absorption tower may be provided one or more times. For example, when producing a liquid mixture using multiple condensers, a first condenser and a second condenser may be used. In this way, when producing a liquid mixture using multiple condensers, the composition of the condensate is simplified, the NIR signal ratio of each component increases, and the accuracy of the analysis can be improved.

[0039] More specifically, the reaction products discharged from the reactor can be supplied to the first condenser, where unreacted liquid condensates such as lactic acid are formed at the bottom of the first condenser and discharged into the lower fraction of the first condenser, while the hard gas and components such as acrylic acid, excluding the unreacted lactic acid, can be discharged into the upper fraction of the first condenser.

[0040] The upper fraction from the first condenser can be supplied to the second condenser. In the second condenser, the reaction products are further condensed and separated into a lower fraction containing acrylic acid and propanoic acid and an upper fraction containing hard gas.

[0041] As described above, in a method for producing a liquid mixture using multiple condensers or absorption towers, the concentration of lactic acid and lactic acid derivatives including lactic acid oligomers discharged to the bottom of the first condenser can be analyzed in step 3 described later, and the concentration of propanoic acid discharged to the bottom of the second condenser can be analyzed in step 3 described later.

[0042] On the other hand, when the first and second condensers are used as described above, the production of the liquid mixture in the first condenser in step 2 may be carried out under temperature conditions of 100°C to 250°C. If carried out at a temperature exceeding 250°C, the gas-phase reaction product may not be able to be liquefied, and the energy required to separate lactic acid derivatives including lactic acid oligomers in subsequent purification steps may increase. If carried out at a temperature below 100°C, the acrylic acid content in the lower fraction of the first condenser may increase, and the acrylic acid recovery rate may decrease. Preferably, the process may be carried out at a temperature of 110°C or higher, 120°C or higher, or 130°C or higher, and 220°C or lower, 200°C or lower, or 180°C or lower.

[0043] In the second condenser, the production of the liquid mixture may be carried out under temperature conditions of 50°C to 150°C. If carried out at a temperature exceeding 150°C, the upper fraction of the first condenser may not be able to be liquefied, and the amount of acrylic acid product lost may increase. If carried out at a temperature below 50°C, excessive energy consumption may become a problem. Preferably, it may be carried out at a temperature of 60°C or higher, 70°C or higher, or 80°C or higher, and 130°C or lower, 120°C or lower, or 110°C or lower.

[0044] (Step 3) Step 3 of the present invention is to continuously pass the liquid mixture prepared in Step 2 through an optical cell and analyze the concentrations of lactic acid, acrylic acid, and propanoic acid in the liquid mixture in real time using a near-infrared spectrometer.

[0045] When the liquid mixture is continuously passed through the optical cell, the probe in the optical cell contacts or interfaces with the liquid mixture stream. The signal thus detected is transmitted to a near-infrared spectrometer to obtain information on each component in the liquid mixture. Subsequently, the generated information is sent to the spectrometer by any means, such as a wired cable, wireless transmission, etc., and the spectrometer generates a spectrum of absorbance against wavelength. The generated spectrum enables the determination of the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid, which are the main components in the sampled liquid mixture stream. Thus, by measuring the near-infrared absorbance at the characteristic wavelengths of each component in the liquid mixture using a near-infrared spectrometer, the concentration, i.e., the composition, of each component in the liquid mixture can be analyzed in real time. The signal generated based on the information of the liquid mixture analyzed in real time enables the control of any step in the overall process of the present invention.

[0046] The near-infrared rays used in the near-infrared spectrometer of the present invention are in the wavelength range of 4,000 cm -1 to 12,500 cm -1 . Generally, the near-infrared absorbance for -CH, -OH, -NH functional groups is known to be rather weak, but the change in absorbance with respect to the change in unit concentration of the near-infrared absorption spectrum is more sensitive than the change in absorbance for visible light (12,000 cm -1 to 25,000 cm -1 ) and mid-infrared (400 cm -1 to 4,000 cm -1 ). Therefore, when using light in the near-infrared region, it is possible to analyze the concentration of the main components without the need for separate treatments such as diluting the sample, and at the same time, it is possible to perform quantitative analysis of multiple components and shorten the analysis time. More preferably, the near-infrared rays can use the wavelength range of 5,400 cm -1 , 6,350 cm -1 , or 7,200 cm -1 to 12,500 cm -1 .

[0047] The near-infrared spectrometer that can be used in this invention is not particularly limited; a typical example is the Bruker MPA II.

[0048] (Step 4) Step 4 of the present invention is a step in which, based on the analysis results of Step 3, one or more of the reaction temperature and catalyst regeneration in Step 1 are determined.

[0049] In the acrylic acid production method by lactic acid dehydration reaction, coking may occur on the catalyst surface due to unreacted lactic acid and lactic acid oligomers during the reaction. This reduces the surface area of ​​the catalytic active species, and if coke accumulates continuously on the catalyst surface, the amount of propanoic acid produced as a byproduct increases, inducing loss of acrylic acid during the purification process, which may make catalyst regeneration impossible or require excessive energy to regenerate. Therefore, in order to ensure the desired lactic acid conversion rate and high yield of acrylic acid while continuously operating step 1 of the present invention, it is important to select a catalyst regeneration step by adjusting the temperature of the dehydration reaction at an appropriate time.

[0050] According to one aspect of the present invention, if the analysis results in step 3 show that the concentrations of lactic acid and lactic acid oligomers in the liquid mixture have increased by 0.5% to 10% by weight compared to the initial reaction conditions, the step in step 1 may include raising the reactor temperature by 1 to 50°C. By increasing the concentrations of lactic acid and lactic acid oligomers, the reactor temperature can be further increased, and the reactor conversion rate can be maintained at a level equivalent to the initial conditions. In other words, in addition to determining the catalyst regeneration step based on the analysis results in step 3, the reaction rate can be controlled and byproduct formation reduced by controlling the reactor temperature. Preferably, if the concentrations of lactic acid and lactic acid oligomers in the liquid mixture have increased by 1.0% to 9.0% by weight or 1.0% to 8.0% by weight compared to the initial reaction conditions, the temperature in step 1 can be adjusted, and the reactor temperature can be raised to 1°C or higher, 2°C or higher, 3°C or higher, 4°C or higher, or 5°C or higher, and 40°C or lower, 30°C or lower, 20°C or lower, or 15°C or lower.

[0051] According to one embodiment of the present invention, the catalyst regeneration step can be performed if the analysis result of step 3 shows that the concentration of propanoic acid in the liquid mixture is 0.1% to 5% by weight. To determine catalyst regeneration, it can be determined by comparing it with a reference substance for determining catalyst regeneration and the reference value of said reference substance. In the present invention, it was confirmed that selecting propanoic acid in the liquid mixture as the reference substance and performing the catalyst regeneration step when the concentration of propanoic acid in the liquid mixture is 0.1% to 5% by weight is desirable from the viewpoint of ease of catalyst regeneration and lifespan. Furthermore, in the purification step to finally obtain acrylic acid, the higher the concentration of propanoic acid, the more difficult it becomes to purify the acrylic acid. To prevent this, it is desirable to regenerate the catalyst within the aforementioned range of propanoic acid concentrations. Preferably, step 4 can be performed when the concentration of propanoic acid in the liquid mixture is 4%, 3%, 2%, 1%, or 0.7%.

[0052] Alternatively, the catalyst regeneration step can be performed by raising the reactor temperature to 320 to 450°C and flowing a mixed gas containing oxygen with an oxygen concentration of 0.1 to 20 mol% to remove coke from the catalyst used in the lactic acid dehydration reaction. If the catalyst regeneration temperature is lower than this, coke regeneration will be incomplete, and if the temperature is higher, the catalyst may be overheated, reducing its lifespan. Furthermore, if the oxygen concentration is lower than the above range, the time required for catalyst regeneration may be delayed, and if the oxygen concentration is higher, the catalyst may be overheated by the heat of coke oxidation, reducing its lifespan. On the other hand, the mixed gas may contain nitrogen, and may further contain steam as needed. Preferably, the reactor temperature during catalyst regeneration may be 350°C or higher, 370°C or higher, 380°C or higher, or 390°C or higher, and 430°C or lower, 420°C or lower, or 410°C or lower. Furthermore, the oxygen concentration of the mixed gas may be 0.5 mol% or more, 1.0 mol% or more, 2.0 mol% or more, or 3.0 mol% or more, and 15 mol% or less, 10 mol% or less, or 7.0 mol% or less.

[0053] Furthermore, the present invention may further include the step of separating a portion of the liquid mixture and performing liquid chromatographic analysis on it. Liquid chromatographic analysis has the advantage of being more accurate than other analytical methods, but it usually has the problem of being time-consuming and making it difficult to respond immediately by analyzing reaction products. In contrast, the present invention makes it possible to increase the reliability of the analysis results from the near-infrared spectrometer by additionally performing the liquid chromatographic analysis on the same sample in addition to the near-infrared spectrometer and directly comparing it with the analysis results from the near-infrared spectrometer.

[0054] Furthermore, in the acrylic acid production method of the present invention described above, the composition of the reactants and reaction products changes in real time in a continuous process. As a result, after comparing the composition of the preparative product measured by liquid chromatography with the error of the product composition measured using a near-infrared spectrometer under normal conditions, the composition of the liquid mixture can be analyzed in real time using a near-infrared spectrometer, as in step 3 of the present invention, to reduce measurement errors. This makes it possible to more accurately determine whether or not there are any abnormalities in the reactor state, such as an increase in the content of lactic acid derivatives including the lactic acid oligomer and / or an increase in the propanoic acid content, and to decide whether or not to proceed to step 4.

[0055] The measurement error of the concentrations of lactic acid, lactic acid oligomer, acrylic acid, and propanoic acid in the liquid mixture, as measured by near-infrared spectrometer and liquid chromatography analysis, is 1.0% or less. Preferably, the measurement error of the concentrations of lactic acid and acrylic acid in the liquid mixture, as measured by the near-infrared spectrometer and liquid chromatography analysis, is 1.0% or less, or 0.9% or less. The reference value for determining the error of each component is determined by repeatedly measuring the same sample by liquid chromatography, using the liquid chromatography analysis results as a reference, setting the average value of these measurements as the reference value, and calculating the error by comparing it with the analysis results of the near-infrared spectrometer.

[0056] On the other hand, the present invention provides a lactic acid dehydration reaction apparatus comprising: dehydration reactors 2, 2a, 2b in which a lactic acid dehydration reaction is carried out in the presence of a catalyst; a discharge unit for discharging reaction products; condensers 3, 3a, 3b connected to the discharge unit for condensing reaction products to produce a liquid mixture; a supply unit for continuously supplying the liquid mixture from an absorption tower or the lower part of a condenser to an optical cell (NIR cell) of a near-infrared spectrometer; a near-infrared spectrometer for real-time analysis of the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the supplied liquid mixture; and a near-infrared analysis signal processing and control device 4.

[0057] For details regarding the catalyst, reaction products, liquid mixture, near-infrared spectrometer, etc., in the lactate dehydration reaction apparatus of the present invention, please refer to the above-mentioned information.

[0058] The reaction section is the area where the dehydration reaction of vaporized lactic acid takes place in the presence of a catalyst, and the reaction product is produced. The reaction section can be a reactor equipped with a heating section as an example, and the reactor may include a supply section for supplying the lactic acid reactant, a vaporization section for vaporizing the aqueous lactic acid solution, and a catalyst section for contacting the vaporized lactic acid molecules with the catalyst.

[0059] The reaction products produced in the reaction section are discharged through a discharge section connected to the reaction section and supplied from the discharge section to an absorption tower or condenser connected to the discharge section, which condenses the reaction products to produce a liquid mixture. The absorption tower or condenser produces the gaseous reaction products in the form of a liquid mixture.

[0060] The form of the absorption column or condenser is not particularly limited, but as an example, it may be initiated in a quenching vessel or a forced evaporation vessel, or it may contain an internal column charge. If an absorption column is used, water or an organic solvent may be used, and an injection nozzle may be provided to bring the reaction product into contact with water within the absorption column to produce a liquid mixture. Polymerization inhibitors may be added to the water or organic solvent to prevent polymerization of acrylic acid.

[0061] A supply unit is provided at the bottom of the absorption tower or condenser, and a liquid mixture is continuously supplied to an optical cell for analysis using a near-infrared spectrometer. The concentration of each component in the liquid mixture passed through the optical cell is measured using the aforementioned near-infrared spectrometer. The concentrations of the products analyzed using the near-infrared spectrometer are transmitted as near-infrared analysis signals to a signal processing and control device. The signal processing and control device determines one or more of the reaction temperature in the reaction section and catalyst regeneration based on the analysis signals, and adjusts the reaction temperature by adjusting the temperature inside the reactor and / or switches the gas phase feed to a mixed gas containing oxygen necessary for catalyst regeneration to regenerate the catalyst.

[0062] Furthermore, the absorption tower or condenser may consist of one or more units, specifically one or two units. A description of multiple absorption towers or condensers is provided above.

[0063] According to one aspect of the present invention, the invention may further include a liquid chromatography analyzer in which at least a portion of the supply unit is branched and connected. As described above, by performing near-infrared spectrometer and liquid chromatography analysis simultaneously, the concentration of each component in the liquid mixture can be analyzed quickly and accurately.

[0064] Figure 1 is a diagram illustrating an example of a process apparatus used in a method for producing acrylic acid by a lactate dehydration reaction according to one embodiment of the present invention.

[0065] Referring to Figure 1, the vaporized high-temperature lactic acid and water vapor, along with a carrier gas as needed, are mixed into a gas phase feed 11 which flows into the dehydration reactor 2. The gas phase product 21 produced in the reactor is fed into the condenser 3 for cooling and separated into a liquid mixture 31 containing acrylic acid and a lightweight gas phase product 32. At this time, the composition of the liquid mixture passing through the NIR cell is transmitted to the NIR signal processing and control device 4 at a frequency of 2 to 3 times per minute (product signal 44a). If the content of lactic acid and lactic acid derivatives, including lactic acid oligomers, falls outside the operating range, the reactor temperature can be controlled (reactor control 42) to bring it back within the operating range. Generally, as the reaction time progresses, the catalyst becomes inactive, the content of lactic acids increases, and the yield of acrylic acid decreases, so the conversion rate and acrylic acid yield are maintained by increasing the reaction temperature. If the conversion rate decreases when the temperature rises above a certain level, or if the propanoic acid content rises above a certain level, the gas phase feed 11 supplied to the reactor can be switched (gas phase feed control 41) to initiate the reactor regeneration step. At this time, the composition of the gas phase feed 11 changes to oxygen and carrier gas, and the reactor temperature is adjusted so that the coke accumulated on the catalyst can be oxidized and vaporized. Steam can be added to the gas phase feed 11 as needed to control the heat generated during the coke oxidation process.

[0066] Figure 2 illustrates a process apparatus using two condensers in the acrylic acid production method by lactic acid dehydration reaction according to the present invention.

[0067] In multi-stage condensation, in condenser 3a, which is operated at a high temperature, the high-boiling-point liquid mixture 33 of lactic acid is first condensed into a liquid, then separated, and the composition content is transmitted to the NIR signal processing and control device 4 via an NIR cell (product signal 44b). The remaining lightweight product 34 in the gas phase is separated into a low-boiling-point liquid mixture 35 such as acrylic acid and a lightweight product 32 in condenser 3b, which is operated at a low temperature, and the composition content of the low-boiling-point liquid mixture 35 is transmitted to the NIR signal processing and control device 4 via an NIR cell (low-boiling-point product signal 44c). Two or more dehydration reactors 2a, 2b can be operated continuously by performing regeneration in the reactor where catalyst regeneration is required (gas phase feed control 41) and operating the remaining reactors. Two or more condensers 3a, 3b can save energy input in the lactic acid separation process by adjusting the temperature of condenser 3a, which is operated at a high temperature (condenser control 43). Specifically, if the content of lactic acid products in the high-boiling point unreacted feed signal 44b, confirmed in the high-boiling point liquid mixture 33 of lactic acids including lactic acid and lactic acid oligomers, is high, or if the content of propanoic acid in the low-boiling point product signal 44c, confirmed in the liquid mixture 35 such as acrylic acid, is high, the reactor temperature can be adjusted or the catalyst can be regenerated. If the content of acrylic acid products in the high-boiling point unreacted feed signal 44b, confirmed in the high-boiling point liquid mixture 33 of lactic acids, is high, or if the content of lactic acid products in the low-boiling point product signal 44c, confirmed in the low-boiling point liquid mixture 35 such as acrylic acid, is high, the temperature of the condenser 3a, which is operated at a high temperature, can be adjusted (condenser control 43). [Effects of the Invention]

[0068] According to the present invention's method and apparatus for producing acrylic acid by lactic acid dehydration reaction, the reactor state can be easily checked and abnormal reactions addressed by continuous measurement of the main products in near real-time. [Brief explanation of the drawing]

[0069] [Figure 1] Figure 1 schematically shows the process and apparatus used in the acrylic acid production method by lactate dehydration reaction according to one embodiment of the present invention. [Figure 2] Figure 2 schematically shows a process and apparatus using two condensers in a method for producing acrylic acid by lactate dehydration reaction according to one embodiment of the present invention. [Modes for carrying out the invention]

[0070] The embodiments of the present invention will be described in more detail below with reference to the following examples. However, the following examples are merely illustrative of embodiments of the present invention, and the content of the present invention is not limited to the following examples.

[0071] Example 1 Acrylic acid was produced by lactic acid dehydration reaction according to the process flowchart shown in Figure 1 and the process conditions in Tables 1 to 3 below. Table 1 below shows the operating conditions of each apparatus during the reaction, and Table 2 below shows the operating conditions of each apparatus during catalyst regeneration. Furthermore, Table 3 below shows a method for controlling the temperature of reactor 2 (reactor control 42) by controlling the composition of the gas phase feed 11 (gas phase feed 41) by changing the composition of the liquid mixture 31, which is the product after condensation.

[0072] Specifically, analysis of the liquid product via a product NIR cell at the start of the reaction revealed that the lactic acid and lactic acid oligomer content was 4.0% by weight. Over time, the lactic acid and lactic acid oligomer content in the liquid product increased by 1.3% by weight, reaching 5.3% by weight. After confirming the increase in the lactic acid and lactic acid oligomer content in the liquid product, the reactor temperature was raised from 352°C to 358°C. This restored the conversion rate, and it was confirmed that the lactic acid and lactic acid oligomer content decreased to 4.2% by weight.

[0073] Subsequently, as the reaction continued, the content of lactic acid and lactic acid oligomers increased to 6.5% by weight, and the content of propanoic acid increased to 0.6% by weight. After confirming this, the reaction temperature was raised to 400°C, and the composition of the gas phase feed was switched to oxygen and nitrogen to proceed to the catalyst regeneration step. [Table 1] [Table 2] [Table 3]

[0074] Example 2 Acrylic acid was produced by lactic acid dehydration reaction according to the process flowchart shown in Figure 2 and the process conditions in Tables 4 to 6 below. Example 2 was operated by adding multi-stage condensation and reactor swing switching operation to Example 1. Table 4 below shows the operating conditions of each apparatus during the reaction, and Table 5 below shows the composition of the gas phase feed supplied to the reactor. Furthermore, Table 6 below shows a method in which the temperature of the dehydration reactor 2 is controlled by the control device 41 to control the reaction gas phase feed 12, the regeneration gas phase feed 13, and the exhaust gas lines of the dehydration reaction product 22 and regenerated exhaust gas 23, which are connected to the respective dehydration reactors 2a and 2b, based on the composition changes 44b and 44c of the high-boiling point liquid mixture 33 and low-boiling point liquid mixture 35, which are the products after condensation, in order to control the temperature of the dehydration reactor 2 (reactor control 42) and control the temperature of the condenser 3a (condenser control 43).

[0075] Specifically, analysis of the liquid product collected in the primary condenser at the start of the reaction via an NIR cell revealed that 10.6% by weight of the total feed was collected, of which 33.4% by weight was lactic acid and lactic acid oligomers. In the secondary condenser, 20.8% by weight of acrylic acid was collected at the start of the reaction. As the reaction time progressed, the weight of acrylic acid collected in the secondary condenser decreased. When the weight of acrylic acid fell below 19.5% by weight, the condensation temperature of the primary condenser was increased by 2-3°C to reduce the proportion of acrylic acid lost in the primary condenser. Over time, the amount of product collected in the primary condenser increased to 11.4% by weight of the total feed, and the content of lactic acid and lactic acid oligomers in the liquid product increased by 6.8% by weight, reaching 40.2% by weight. The initial temperature of the primary condenser was 125°C and was raised to 130°C before the reactor temperature was increased. After confirming an increase in the lactic acid and lactic acid oligomer content in the liquid product, the reactor temperature was raised from 352°C to 358°C. This restored the conversion rate, reducing the amount of product collected in the primary condenser to 10.5% by weight of the total feed, and confirming a reduction in the lactic acid and lactic acid oligomer content in the feed to 35.4% by weight. Simultaneously, the primary condenser temperature was lowered to 127°C.

[0076] Subsequently, as the reaction continued, the amount of product collected in the primary condenser increased to 13.7% by weight of the total feed, the content of lactic acid and lactic acid oligomers in the feed increased to 41.5% by weight, and the propanoic acid content in the product collected in the secondary condenser increased to 0.6% by weight. After confirming this, the connection of the dehydration reactor 2a was switched from the reaction feed containing lactic acid to the regenerative feed containing oxygen, and then the condenser was switched to exhaust gas. The reaction temperature was then raised to 400°C to proceed to the catalyst regeneration step. The temperature of the primary condenser was adjusted by checking the acrylic acid yield, as before raising the reactor temperature, and the final temperature of the primary condenser just before proceeding to the regeneration step was 133°C.

[0077] [Table 4]

[0078] [Table 5]

[0079] [Table 6]

[0080] Experimental Example 1 In the process flowcharts shown in Figures 1 and 2, portions of the liquid mixture were taken through branched lines 36a, 36b, and 36c and subjected to liquid chromatography analysis. The results were compared with the NIR analysis results and are shown in Table 7.

[0081] In Table 7 below, Example 1 involves calibration by introducing the reaction product (A), whose content was determined by liquid chromatography, and a sample (B) obtained by adding a standard substance to the reaction product and performing a spike test, into NIR analysis equipment under steady state. Example 2 involves calibration using the reaction product (A) introduced under steady state and the product (C) collected by real-time NIR analysis. Example 3 involves calibration using all three samples A, B, and C. [Table 7]

[0082] As can be seen in Table 7 above, it was confirmed that the prediction error changes depending on the calibration curve learning method. Specifically, in Case 1, the measurement error increased to a maximum of 2.4% by weight, but in Case 2, when products collected by real-time NIR analysis were used, the measurement error decreased to 1.0% by weight or less, and in Case 3, when calibration was performed using all samples, the maximum measurement error was maintained at 1.0% by weight or less, and it was confirmed that the prediction error further decreased for major components such as lactic acid, acrylic acid, and acetaldehyde. [Explanation of Symbols]

[0083] 11: Gas-phase feed (lactic acid, water vapor, and carrier gas during reaction; oxygen and carrier gas during regeneration) 12: Reaction gas phase feed (lactic acid, water vapor, and carrier gas) 13: Regenerative gas phase feed (oxygen and carrier gas) 2, 2a, 2b: Dehydration reactor 21: Gas-phase products (dehydration reaction products during the reaction; exhaust gas after regeneration during regeneration) 22: Dehydration reaction products 23: Emissions after regeneration 3, 3a, 3b: Condenser 31: Liquid mixture 32, 34: Lightweight products 33: High boiling point liquid mixtures 35: Low boiling point liquid mixtures 4: Near-infrared analysis signal processing and control device 41: Gas-phase feed control (reaction / regeneration) 42: Reactor control 43: Control of the condenser 44a: Product signals (lactic acid, lactate oligomers, and propanoic acid) 44b: Feed signal of unreacted substances at high boiling points (lactic acid, lactic acid oligomer) 44c: Low boiling point product signal (propanoic acid)

Claims

1. Step 1: To produce a reaction product containing acrylic acid by a lactate dehydration reaction in the presence of a catalyst; Step 2: Condensing the reaction product to produce a liquid mixture; Step 3: Continuously pass the liquid mixture through an optical cell and analyze the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in the liquid mixture in real time using a near-infrared spectrometer; and Step 4 includes a step (determining one or more of the reaction temperature and catalyst regeneration in Step 1 based on the analysis results in Step 3, A method for producing acrylic acid by lactic acid dehydration reaction.

2. In step 1, lactic acid is supplied in aqueous solution form. The concentration of the lactic acid aqueous solution is 10% by weight to 80% by weight. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

3. The reaction in step 1 is carried out under temperature conditions of 300°C to 500°C and pressure conditions of 1 to 5 atmospheres. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

4. The production of the liquid mixture in step 2 is carried out under temperature conditions of 50°C to 250°C. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

5. The production of the liquid mixture in step 2 is carried out in one condenser; or in a first condenser and a second condenser. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

6. The production of the liquid mixture in step 2 is carried out in the first condenser and the second condenser. In the first condenser, the production of the liquid mixture is carried out under temperature conditions of 100°C to 250°C. In the second condenser, the liquid mixture is produced under temperature conditions of 50°C to 150°C. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 5.

7. The near-infrared light used in the near-infrared spectrometer in step 3 is 4000 cm². －１ ~12500cm －１ Using the wavelength range, A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

8. If the analysis results from step 3 indicate that the concentration of lactic acid and lactic acid derivatives including lactic acid oligomers in the liquid mixture has increased by 0.5% to 10% by weight compared to the initial reaction conditions, the step includes raising the temperature of the reactor in step 1 by 1°C to 50°C. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

9. If the analysis result in step 3 indicates that the concentration of propanoic acid in the liquid mixture is 0.1% to 5% by weight, the catalyst regeneration step is performed. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

10. The catalyst regeneration step is carried out by raising the reactor temperature to 320 to 450°C and flowing a mixed gas containing oxygen with an oxygen concentration of 0.1 to 20 mol% to remove coke. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 9.

11. The further step includes separating a portion of the liquid mixture and performing liquid chromatography analysis on it. A method for producing acrylic acid by a lactate dehydration reaction as described in claim 1.

12. The measurement error of the concentrations of lactic acid, lactic acid oligomer, acrylic acid, and propanoic acid in the liquid mixture, as measured by near-infrared spectrometer and liquid chromatography analysis, is 1.0% or less. A method for producing acrylic acid by a lactate dehydration reaction according to claim 11.

13. A reaction chamber in which the lactate dehydration reaction takes place in the presence of a catalyst; Discharge section for discharging reaction products; An absorption tower or condenser connected to the aforementioned discharge section, which condenses the reaction products to produce a liquid mixture; A supply unit that continuously supplies the aforementioned liquid mixture from the bottom of the absorption tower or condenser to the optical cell of a near-infrared spectrometer; A near-infrared spectrometer for real-time analysis of the concentrations of lactic acid, lactic acid derivatives including lactic acid oligomers, acrylic acid, and propanoic acid in a supplied liquid mixture; and Including near-infrared analysis signal processing and control equipment, Lactate dehydration reactor.

14. The absorption tower or condenser consists of one or two units. The lactate dehydration reaction apparatus according to claim 13.

15. The liquid chromatography analyzer further includes a part of the supply unit that is branched and connected, The lactate dehydration reaction apparatus according to claim 13.

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