Method and apparatus for producing acrylic acid

Abstract

The present invention relates to a method and apparatus for producing acrylic acid. Specifically, it relates to a method and apparatus for producing acrylic acid, including a two-stage reactor that enables the acrylic acid yield to reach a target level.

Description

Technical Field

[0007] , , ,

[0006]

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0176547 filed on December 7, 2023 and Korean Patent Application No. 10 - 2024 - 0177830 filed on December 3, 2024, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a method and an apparatus for producing acrylic acid. Specifically, it relates to a method and an apparatus for producing acrylic acid including a two - stage reactor capable of achieving a target level of acrylic acid yield.

Background Art

[0003] Acrylic acid is an organic compound having both a carboxylic acid and an unsaturated double bond in the molecule. Its structure is very simple and it can be converted into various substances, and since it can be polymerized, it is used in various industrial fields.

[0004] Specifically, acrylic acid may be used as polyacrylic acid required for the production of superabsorbent polymers, adhesive adhesives, paints, etc., or as a raw material for producing other forms of acrylate - series monomers, or as a polymerization raw material with other various monomers such as acrylamide, acrylonitrile, styrene, and alpha - olefins.

[0005] Such acrylic acid is generally produced by using propylene generated in the refining and separation processes of crude oil, such as naphtha cracking.

[0006] However, recently, as the depletion of crude oil and the interest in environmental problems have increased, the interest in methods for producing acrylic acid using environmentally friendly raw materials has been increasing.

[0007] Conventional methods for producing acrylic acid by the gas-phase dehydration reaction of lactic acid on an acid catalyst involve not only the main reaction of acrylic acid production but also numerous side reactions. Therefore, it is necessary to design appropriate reaction conditions and reactors to obtain a desirable yield of acrylic acid. [Overview of the project] [Problems that the invention aims to solve]

[0008] This specification aims to provide a method for producing acrylic acid, including a two-stage reactor designed to achieve a desired yield of acrylic acid through a lactate dehydration reaction, and the apparatus for that method. [Means for solving the problem]

[0009] This disclosure provides an apparatus for producing acrylic acid, comprising a two-stage reactor for a lactate dehydration reaction, a feed supply unit for supplying lactic acid gas, a first-stage dehydration reactor filled with a catalyst for the lactate dehydration reaction, and a second-stage dehydration reactor filled with a catalyst for the lactate dehydration reaction, satisfying the following formula 1.

number

[0010] For example, the yield of acrylic acid obtained in the acrylic acid production apparatus can be 53 mol% or more.

[0011] In one example, the first-stage dehydration reactor and the second-stage dehydration reactor are connected by a transfer line, the transfer line may further include a heating section.

[0012] On the other hand, this disclosure provides a method for producing acrylic acid that includes a first stage in which a feedstream containing lactic acid gas molecules is supplied from a feed supply unit to the upper stage of a first-stage dehydration reactor filled with a catalyst, and after the dehydration reaction proceeds, the stream is discharged from the lower stage; and a second stage in which the stream discharged from the lower stage of the first-stage dehydration reactor is supplied to the upper stage of a second-stage dehydration reactor filled with a catalyst, and after the dehydration reaction proceeds, the stream is discharged from the lower stage, wherein the feedstream supplied to the upper stage of the first-stage dehydration reactor contains lactic acid gas and satisfies the following formula 2.

number

[0013] For example, the method for producing acrylic acid can yield acrylic acid at a yield of 53 mol% or more.

[0014] For example, the stream discharged from the lower stage of the first-stage dehydration reactor is transferred to the second-stage dehydration reactor via a transfer line, and the temperature of the stream can be maintained between 370°C and 410°C during the transfer.

[0015] In this 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. Furthermore, the terms used herein are used solely to illustrate exemplary embodiments and are not intended to limit the invention.

[0016] A singular expression includes plural forms unless the context clearly indicates a different meaning.

[0017] As used herein, terms such as "comprising," "including," or "having" are for the purpose of describing implemented features, numbers, steps, components, or combinations thereof, and do not exclude one or more other features, numbers, steps, components, combinations thereof, or the possibility of addition.

[0018] Also, in this specification, when it is mentioned that each layer or element is "formed on" each layer or element, it means that each layer or element is directly formed on each layer or element, or it means that other layers or elements can be additionally formed between each layer, on the object, or on the substrate.

[0019] Since the present invention can be subject to various modifications and can have various forms, specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, and it should be understood that the present invention includes all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0020] In the gas-phase dehydration reaction of lactic acid, generally, vaporized lactic acid is introduced into a reactor filled with a catalyst, and a dehydration reaction occurs. The acrylic acid generated in the dehydration reaction is discharged from the lower stage of the reactor.

[0021] In such a process for producing acrylic acid through the gas-phase dehydration reaction of lactic acid, not only acrylic acid, which is the product of the main reaction, but also numerous by-products from a large number of side reactions are generated together. Therefore, it is necessary to design appropriate reaction conditions and reactors so as to obtain the desired acrylic acid yield.

[0022] Therefore, in the present disclosure, there is an attempt to provide a method for producing acrylic acid and an apparatus thereof, including a two-stage reactor designed to achieve the desired acrylic acid yield in the production of acrylic acid.

[0023] Specifically, the present disclosure aims to provide a method for producing acrylic acid and an apparatus therefor, which controls the length of the catalyst stage included in a two-stage reactor or the average residence time of the stream in the reactor including the catalyst stage to obtain a desired acrylic acid yield.

[0024] Hereinafter, the apparatus for producing acrylic acid according to the present disclosure will be described.

[0025] According to one aspect of the present disclosure, in a two-stage reactor for a lactic acid dehydration reaction, there can be provided an apparatus for producing acrylic acid including a feed supply section to which a lactic acid gas is supplied, a first-stage dehydration reactor filled with a catalyst for a lactic acid dehydration reaction, and a second-stage dehydration reactor filled with a catalyst for a lactic acid dehydration reaction (see FIG. 1).

[0026] Further, the apparatus for producing acrylic acid according to the present disclosure can satisfy the following mathematical formula 1.

Equation

[0027] That is, in the case of an apparatus for producing acrylic acid in which the length of the first stage satisfies the range of 0.3 or more to 0.6 or less with respect to the length of the entire reaction stage, the yield of acrylic acid obtained from the production apparatus can be 53 mol% or more. At this time, the yield of acrylic acid can be obtained by the following mathematical formula 3. [Mathematical formula 3] Acrylic acid yield (mol%) = (number of moles of acrylic acid produced in the second-stage reactor / number of moles of lactic acid introduced into the first-stage reactor) × 100

[0028] The number of moles of acrylic acid produced in the second-stage reactor is measured as the number of moles of acrylic acid in the discharge stream of the second-stage reactor, and the number of moles of lactic acid introduced into the first-stage reactor is measured as the number of moles of lactic acid in the feed stream introduced into the first-stage reactor.

[0029] Setting the desired acrylic acid yield to 53 mol% or higher represents the highest acrylic acid yield currently achievable in the process. Since a higher acrylic acid yield reduces the unit consumption, a higher acrylic acid yield is desirable. Specifically, increasing the acrylic acid yield from 50 mol% to 53 mol% reduces the lactic acid unit consumption by approximately 5-6%. The lactic acid unit consumption accounts for the largest portion of the manufacturing cost of acrylic acid, so improving the acrylic acid yield is crucial for cost reduction. In this case, the lactic acid unit consumption is calculated by dividing the total amount of lactic acid (kg) input into the process by the amount of acrylic acid (kg) produced. A lower lactic acid unit consumption indicates a more economical process.

[0030] The first-stage dehydration reactor and the second-stage dehydration reactor can be arranged sequentially in an orderly fashion, one above the other.

[0031] The upper part of the first-stage dehydration reactor is connected to a feed supply unit to which lactic acid gas is supplied. The dehydration catalyst packed into the first-stage dehydration reactor may include one or more catalysts selected from the group consisting of calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts. Other reaction conditions can be used without particular limitation as long as they are commonly used in the art to which the present invention belongs and do not conflict with the limitations specified herein.

[0032] More specifically, examples of the dehydration catalyst include CaSO4 / Na2SO4;Na4P2O7 / CaSO4;Na4P2O7 / Ca3(PO4)2;NaH2PO4-NaHCO3 / SiO2;AlPO4-NH3;Ca3(PO4)2 / CaSO4;Ca2P2O7;Ca5(PO4)3(OH).

[0033] The lower stage of the first-stage dehydration reactor may include a transfer line connected to the upper stage of the second-stage dehydration reactor. Furthermore, this transfer line may include a heating section. The lactic acid dehydration reaction is a high-temperature reaction. Therefore, if the temperature of the stream discharged from the first-stage dehydration reactor decreases during the transfer to the second-stage dehydration reactor, heat loss for the dehydration reaction occurs. To raise the temperature of the discharged stream to the dehydration reaction temperature, the transfer line may include a heating section.

[0034] For example, the stream discharged from the first-stage reactor may have a temperature of approximately 350-360°C, and as the stream passes through the transfer line, it can be heated to approximately 390°C by a heating unit before being fed into the second-stage reactor.

[0035] The upper section of the second-stage dehydration reactor is connected to a transfer line for transporting the stream discharged from the first-stage dehydration reactor. The dehydration catalyst packed into the second-stage dehydration reactor may include one or more catalysts selected from the group consisting of calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts. Other reaction conditions can be used without particular limitation, as long as they are commonly used in the art to which the present invention pertains and do not conflict with the limitations specified herein.

[0036] More specifically, examples of the dehydration catalyst include CaSO4 / Na2SO4;Na4P2O7 / CaSO4;Na4P2O7 / Ca3(PO4)2;NaH2PO4-NaHCO3 / SiO2;AlPO4-NH3;Ca3(PO4)2 / CaSO4;Ca2P2O7;Ca5(PO4)3(OH).

[0037] In the second-stage dehydration reactor, after the additional dehydration reaction proceeds, the product stream is discharged from the lower stage. Therefore, a discharge line can be connected to the lower stage of the second-stage dehydration reactor.

[0038] Furthermore, the product stream discharged from the second-stage dehydration reactor can be moved to a condenser along the discharge line. In the condenser, acrylic acid contained in the product stream in a gaseous state can be condensed, liquefied, and collected.

[0039] The method for producing acrylic acid according to this disclosure will be described below, step by step.

[0040] [Phase 1] The first step of this disclosure is to supply a feedstream from a feed supply unit to the upper stage of a first-stage dehydration reactor filled with a catalyst, carry out the lactate dehydration reaction, and then discharge the stream from the lower stage.

[0041] The feedstream supplied to the upper stage of the first-stage dehydration reactor may contain vaporized lactic acid gas molecules. For example, vaporized lactic acid molecules can be obtained by supplying a lactic acid-containing stream to a vaporization reactor and allowing the lactic acid vaporization reaction to proceed inside the vaporization reactor.

[0042] The catalyst packed into the first-stage dehydration reactor may include one or more catalysts selected from the group consisting of calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts as catalysts for the lactate dehydration reaction. Other reaction conditions can be used without particular limitation, as long as they are commonly used in the art to which the present invention belongs and do not conflict with the limitations of this specification.

[0043] More specifically, examples of the dehydration catalyst include CaSO4 / Na2SO4;Na4P2O7 / CaSO4;Na4P2O7 / Ca3(PO4)2;NaH2PO4-NaHCO3 / SiO2;AlPO4-NH3;Ca3(PO4)2 / CaSO4;Ca2P2O7;Ca5(PO4)3(OH).

[0044] The average dehydration reaction temperature of the first-stage dehydration reactor can be carried out under temperature conditions of above 340°C and below approximately 400°C, preferably above 340°C, or above 345°C, or above 350°C, or above approximately 355°C, or below approximately 400°C, or below approximately 390°C, or below approximately 380°C.

[0045] If the dehydration reaction temperature is too low, problems may arise such as a significant decrease in the lactic acid conversion rate and acrylic acid yield. Conversely, if the dehydration reaction temperature is too high, problems may arise such as an increase in byproducts, due to further acceleration of reactions such as i) aldehyde formation by carboxylation or decarbonylation, and ii) propanoic acid formation.

[0046] The stream that has undergone dehydration can be discharged from the lower stage of the first-stage dehydration reactor, and the stream discharged from the lower stage of the first-stage dehydration reactor can be transferred to the second-stage dehydration reactor via a transfer line.

[0047] The stream discharged from the lower stage of the first-stage dehydration reactor may contain acrylic acid in the gas phase produced by the lactate dehydration reaction, unreacted lactic acid gas molecules, and by-products (e.g., acetaldehyde, proponic acid, 2,3-pentanedione, etc.).

[0048] The transfer line is equipped with a heating section, which allows the temperature of the stream discharged from the first-stage dehydration reactor to be maintained between 370°C and 410°C while it is being transferred through the transfer line to the second-stage reactor. The heating section may be a separate heating device, such as a heat exchanger or a hitting band.

[0049] The lactate dehydration reaction is a high-temperature reaction. Therefore, if the temperature of the stream discharged from the first-stage dehydration reactor decreases during the transfer to the second-stage dehydration reactor, heat loss for the dehydration reaction will occur. To raise the temperature of the discharged stream to the dehydration reaction temperature, the transfer line must be able to maintain the aforementioned temperature range.

[0050] [Phase 2] The second stage of this disclosure is to supply the stream discharged from the lower stage of the first stage dehydration reactor to the upper stage of the second stage dehydration reactor which is filled with a catalyst, to allow the dehydration reaction to proceed, and then to discharge the stream from the lower stage.

[0051] The stream discharged from the lower stage of the first-stage dehydration reactor and supplied to the upper stage of the second-stage dehydration reactor may contain unreacted lactic acid gas molecules. Furthermore, the stream discharged from the lower stage of the first-stage dehydration reactor can be supplied to the upper stage of the second-stage dehydration reactor via a transfer line.

[0052] The catalyst packed into the second-stage dehydration reactor may include one or more catalysts selected from the group consisting of calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts as catalysts for the lactate dehydration reaction. Other reaction conditions can be used without particular limitation, as long as they are commonly used in the art to which the present invention belongs and do not conflict with the limitations specified herein.

[0053] More specifically, examples of the dehydration catalyst include CaSO4 / Na2SO4;Na4P2O7 / CaSO4;Na4P2O7 / Ca3(PO4)2;NaH2PO4-NaHCO3 / SiO2;AlPO4-NH3;Ca3(PO4)2 / CaSO4;Ca2P2O7;Ca5(PO4)3(OH).

[0054] The average dehydration reaction temperature of the second-stage dehydration reactor can be controlled under temperature conditions of over 340°C and about 400°C or less, preferably over 340°C, or about 345°C or more, or about 350°C or more, or about 355°C or more, or up to about 400°C, or about 390°C or less, or about 380°C or less.

[0055] If the dehydration reaction temperature is too low, problems may arise such as a significant decrease in the lactic acid conversion rate and acrylic acid yield. Conversely, if the dehydration reaction temperature is too high, problems may arise such as an increase in byproducts, as i) aldehyde formation reactions by carboxylation or decarbonylation, and ii) propanoic acid formation reactions are further accelerated.

[0056] In the second-stage dehydration reactor, after the additional dehydration reaction proceeds, the product stream is discharged from the lower stage. Therefore, a discharge line is connected to the lower stage of the second-stage dehydration reactor to discharge the product stream.

[0057] Furthermore, the product stream discharged from the second-stage dehydration reactor can be moved to a condenser along the discharge line. In the condenser, acrylic acid contained in the product stream in a gaseous state can be condensed, liquefied, and collected.

[0058] Furthermore, the method for producing acrylic acid according to this disclosure can satisfy the following formula 2.

number

[0059] In other words, in a method for producing acrylic acid in which the time the feedstream remains in the first-stage dehydration reactor relative to the total reaction time is in the range of 0.3 to 0.6, the yield of acrylic acid obtained by this method can be 53 mol% or more. At this time, the yield of acrylic acid can be calculated using the following formula 3. [Formula 3] Acrylic acid yield (mol%) = (Number of moles of acrylic acid produced in the second stage reactor / Number of moles of lactate added to the first stage reactor) × 100

[0060] The number of moles of acrylic acid produced in the second-stage reactor was measured in the discharge stream of the second-stage reactor, while the number of moles of lactate introduced into the first-stage reactor was measured in the feedstream introduced into the first-stage reactor.

[0061] Setting the desired acrylic acid yield to 53 mol% or higher represents the highest acrylic acid yield currently achieved in the process. Since a higher acrylic acid yield reduces the unit consumption, a higher acrylic acid yield is desirable. Specifically, increasing the acrylic acid yield from 50 mol% to 53 mol% will reduce the lactic acid unit consumption by approximately 5-6%. The lactic acid unit consumption accounts for the largest portion of the manufacturing cost of acrylic acid, so improving the acrylic acid yield is crucial for cost reduction. In this case, the lactic acid unit consumption is calculated by dividing the total amount of lactic acid (kg) input into the process by the amount of acrylic acid (kg) produced. A lower lactic acid unit consumption indicates a more economical process.

[0062] Furthermore, in the case of a dehydration reaction using lactic acid gas, a fixed-bed cylindrical reactor is used, and the catalyst stage length of the catalyst packed inside this fixed-bed cylindrical reactor is the same as the reactor length. Also, although the first-stage reactor and the second-stage reactor have the same diameter, the catalyst stage length, i.e., the reactor length, is different. In other words, the first-stage and second-stage reactors for the dehydration reaction of this disclosure are each fixed-bed cylindrical reactors, and the time the stream remains in the first-stage or second-stage reactor is proportional to the respective catalyst stage length, i.e., the reactor length. [Effects of the Invention]

[0063] According to one example of the present invention, by configuring the acrylic acid production apparatus with a two-stage reactor and controlling the length of the reaction stage, acrylic acid can be obtained in a target yield.

[0064] Furthermore, according to one example of the present invention, acrylic acid can be obtained in a target yield by using a two-stage reactor during the production of acrylic acid and controlling the residence time in the reactor stream. [Brief explanation of the drawing]

[0065] [Figure 1] This is a schematic diagram of an acrylic acid production apparatus according to one embodiment of the present invention. [Figure 2] This graph shows the yield of acrylic acid according to Formula 1 in one embodiment of the present invention. [Modes for carrying out the invention]

[0066] The operation and effects of the invention will be further described below through specific embodiments of the invention. However, these embodiments are presented merely as examples of the invention and do not determine the scope of the invention's rights.

[0067] [Preparation of the gas-phase lactate feedstream] As the lactic acid raw material, an 88% by weight lactic acid aqueous solution (product name: PURAC H888, obtained from Corbion) was prepared. The lactic acid raw material and distilled water were mixed in a 1:1.2 weight ratio and refluxed for approximately 18 hours at a temperature of approximately 95°C to obtain an approximately 40% by weight lactic acid aqueous solution in which lactic acid and lactic acid oligomers were in equilibrium. This was used as the feed for lactic acid vaporization. Nitrogen was used as the carrier gas, and the internal temperature of the vaporization reactor was set to 200°C to 300°C. The lactic acid molecule feed vaporized in the vaporization reactor was used as the feed for the dehydration reaction.

[0068] Experimental Example 1 [Example 1] The two-stage dehydration reactors for the dehydration reaction were each filled with a dehydration catalyst as a fixed-bed reactor. The first-stage dehydration reactor had a length of 1.5 m and an inner diameter of 4 m. The length and inner diameter of the second-stage dehydration reactor were configured to be the same as the first-stage dehydration reactor. Therefore, the value of Equation 1 was 0.5. Hastelloy material was used for both the first and second-stage dehydration reactors. In addition, the dehydration catalyst was packed into both the first and second-stage dehydration reactors.

[0069] The upper part of the first-stage dehydration reactor was equipped with a feedstream supply unit, through which vaporized lactic acid molecules were supplied. A transfer line was provided between the first-stage and second-stage dehydration reactors, and a temperature controller maintained the temperature at 390°C. A shell-and-tube type heat exchanger was used as the temperature controller. In addition, a discharge line was provided at the lower part of the second-stage dehydration reactor to discharge the dehydrated reaction product.

[0070] As the dehydration catalyst, a calcium phosphate-based catalyst in the form of a composite phase consisting of Ca2P2O7 and Ca5(PO4)3(OH), formed into cylindrical pellets approximately 3 mm in diameter and 3 mm in length, was used. At this time, the mixed weight ratio of Ca2P2O7 to Ca5(PO4)3(OH) was 7:3.

[0071] A vaporized lactic acid feedstream at a temperature of 390°C was supplied to the upper stage of the first-stage dehydration reactor. The residence time of the vaporized lactic acid feedstream inside the first-stage dehydration reactor was 0.8 seconds. At this time, the temperature drop in the first-stage dehydration reactor was 38.4°C, and the discharge temperature from the first-stage dehydration reactor was 351.6°C.

[0072] The stream that had reacted in the first-stage dehydration reactor was transferred to the second-stage dehydration reactor via a transfer line. At this time, the temperature of the stream immediately discharged from the first-stage dehydration reactor was 351.6°C. Therefore, in the transfer line connected to the lower part of the first-stage dehydration reactor, the stream discharged from the first-stage dehydration reactor was heated so that its temperature reached 390°C when it was introduced into the second-stage dehydration reactor.

[0073] At this time, the residence time of the stream transferred from the first-stage dehydration reactor inside the second-stage dehydration reactor was 0.75 seconds. Therefore, the value of Equation 2 was 0.51.

[0074] The product stream, which had undergone dehydration in the second-stage dehydration reactor, was discharged through the discharge line at a temperature of 368.8°C.

[0075] The product stream discharged from the second-stage dehydration reactor was collected and quantitatively analyzed by high-performance liquid chromatography (HPLC) to calculate the yield of acrylic acid and the conversion rate to lactate.

[0076] High-performance liquid chromatography was used for analysis as follows:

[0077] The obtained reaction product was diluted 20-fold by volume using distilled water, and then quantitatively analyzed using HPLC with an Agilent 1260 Infinity II. The HPLC analysis conditions were as follows. -Eluent: 0.005 mol H2SO4 (aq) -Eluent flow rate: 0.4 mL / min -Column: Aminex HPX-87H -Column temperature: 10℃ -Detector: UV 210~300nm -Analysis time: 70 min -Analysis pressure: ~70 bar

[0078] The acrylic acid yield was calculated using the following formula 3. [Formula 3] Acrylic acid yield (mol%) = (Number of moles of acrylic acid produced in the second stage reactor / Number of moles of lactate added to the first stage reactor) × 100

[0079] The number of moles of acrylic acid produced in the second-stage reactor was measured in the discharge stream of the second-stage reactor, while the number of moles of lactate introduced into the first-stage reactor was measured in the feedstream introduced into the first-stage reactor.

[0080] The lactic acid conversion rate was calculated using the following formula 4. [Equation 4] Lactic acid conversion rate (%) = {Amount of lactic acid input (kg / hr) - Lactic acid flow rate at the outlet of the second stage reactor (kg / hr)} / Amount of lactic acid input (kg / hr) × 100

[0081] [Example 2] The two-stage dehydration reactors for the dehydration reaction were each packed with a dehydration catalyst as a fixed-bed reactor. The first-stage dehydration reactor had a length of 1 m and an inner diameter of 4 m. The second-stage dehydration reactor had a length of 2 m and an inner diameter of 4 m. Therefore, the value of Equation 1 was approximately 0.33. Hastelloy material was used for both the first and second-stage dehydration reactors. In addition, the dehydration catalyst was packed into both the first and second-stage dehydration reactors.

[0082] The upper section of the first-stage dehydration reactor was equipped with a feedstream supply unit, through which vaporized lactic acid molecules were supplied. A transfer line was provided between the first-stage and second-stage dehydration reactors, and a temperature controller maintained the temperature at 390°C. A shell-and-tube type heat exchanger was used as the temperature controller. The lower section of the second-stage dehydration reactor was equipped with a discharge line to discharge the dehydrated reaction product.

[0083] As the dehydration catalyst, a calcium phosphate-based catalyst in the form of a composite phase consisting of Ca2P2O7 and Ca5(PO4)3(OH), formed into cylindrical pellets approximately 3 mm in diameter and 3 mm in length, was used. At this time, the mixed weight ratio of Ca2P2O7 to Ca5(PO4)3(OH) was 7:3.

[0084] A vaporized lactic acid feedstream at a temperature of 390°C was supplied to the upper stage of the first-stage dehydration reactor. The residence time of the vaporized lactic acid feedstream inside the first-stage dehydration reactor was 0.5 seconds. At this time, the temperature drop in the first-stage dehydration reactor was approximately 33°C, and the discharge temperature from the first-stage dehydration reactor was 357°C.

[0085] The stream that had reacted in the first-stage dehydration reactor was transferred to the second-stage dehydration reactor via a transfer line. At this time, the temperature of the stream immediately discharged from the first-stage dehydration reactor was 357°C. Therefore, the stream discharged from the first-stage dehydration reactor was heated in a transfer line connected to the lower part of the first-stage dehydration reactor so that its temperature reached 390°C when it was introduced into the second-stage dehydration reactor.

[0086] At this time, the residence time of the stream transferred from the first-stage dehydration reactor inside the second-stage dehydration reactor was 1 second. Therefore, the value of Equation 2 was 0.33.

[0087] The product stream, which had undergone dehydration in the second-stage dehydration reactor, was discharged through the discharge line at a temperature of 363°C.

[0088] The product stream discharged from the second-stage dehydration reactor was collected and quantitatively analyzed by high-performance liquid chromatography (HPLC), and the yield of acrylic acid and the lactic acid conversion rate were calculated as in Example 1.

[0089] [Example 3] The two-stage dehydration reactors for the dehydration reaction were both fixed-bed reactors, packed with dehydration catalysts. The first-stage dehydration reactor had a length of 1.7 m and an inner diameter of 4 m. The second-stage dehydration reactor had a length of 1.3 m and an inner diameter of 4 m. Therefore, the value of Equation 1 was 0.57. Hastelloy material was used for both the first and second-stage dehydration reactors. In addition, dehydration catalysts were packed into both the first and second-stage dehydration reactors.

[0090] The upper section of the first-stage dehydration reactor was equipped with a feedstream supply unit, through which vaporized lactic acid molecules were supplied. A transfer line was provided between the first-stage and second-stage dehydration reactors, and a temperature controller maintained the temperature at 390°C. A shell-and-tube type heat exchanger was used as the temperature controller. In addition, a discharge line was provided in the lower section of the second-stage dehydration reactor to discharge the reaction product after the dehydration reaction.

[0091] As the dehydration catalyst, a calcium phosphate-based catalyst in the form of a composite phase consisting of Ca2P2O7 and Ca5(PO4)3(OH), formed into cylindrical pellets approximately 3 mm in diameter and 3 mm in length, was used. At this time, the mixed weight ratio of Ca2P2O7 to Ca5(PO4)3(OH) was 7:3.

[0092] A vaporized lactic acid feedstream at a temperature of 390°C was supplied to the upper stage of the first-stage dehydration reactor. The residence time of the vaporized lactic acid feedstream inside the first-stage dehydration reactor was 0.9 seconds. At this time, the temperature drop in the first-stage dehydration reactor was approximately 40°C, and the discharge temperature from the first-stage dehydration reactor was 350°C.

[0093] The stream that had reacted in the first-stage dehydration reactor was transferred to the second-stage dehydration reactor via a transfer line. At this time, the temperature of the stream immediately discharged from the first-stage dehydration reactor was 350°C. Therefore, the stream discharged from the first-stage dehydration reactor was heated in a transfer line connected to the lower part of the first-stage dehydration reactor so that its temperature reached 390°C when it was introduced into the second-stage dehydration reactor.

[0094] At this time, the residence time of the stream transferred from the first-stage dehydration reactor inside the second-stage dehydration reactor was 0.64 seconds. Therefore, the value of Equation 2 was 0.58.

[0095] The product stream, which had undergone dehydration in the second-stage dehydration reactor, was discharged through the discharge line at a temperature of 371°C.

[0096] The product stream discharged from the second-stage dehydration reactor was collected and quantitatively analyzed by high-performance liquid chromatography (HPLC), and the yield of acrylic acid and the lactic acid conversion rate were calculated as in Example 1.

[0097] [Comparative Example 1] The two-stage dehydration reactors for the dehydration reaction were both fixed-bed reactors, each packed with a dehydration catalyst. The first-stage dehydration reactor had a length of 0.2 m and an inner diameter of 4 m. The second-stage dehydration reactor had a length of 2.8 m and an inner diameter of 4 m. Therefore, the value of Equation 1 was 0.07. Hastelloy material was used for both the first and second-stage dehydration reactors. In addition, the dehydration catalyst was packed into both the first and second-stage dehydration reactors.

[0098] The upper section of the first-stage dehydration reactor was equipped with a feedstream supply unit, through which vaporized lactic acid molecules were supplied. A transfer line was provided between the first-stage and second-stage dehydration reactors, and a temperature controller was used to maintain a temperature of 390°C. A shell-and-tube type heat exchanger was used as the temperature controller. In addition, a discharge line was provided in the lower section of the second-stage dehydration reactor to discharge the reaction product after the dehydration reaction.

[0099] As the dehydration catalyst, a calcium phosphate-based catalyst in the form of a composite phase consisting of Ca2P2O7 and Ca5(PO4)3(OH), formed into cylindrical pellets approximately 3 mm in diameter and 3 mm in length, was used. At this time, the mixed weight ratio of Ca2P2O7 to Ca5(PO4)3(OH) was 7:3.

[0100] A vaporized lactic acid feedstream at a temperature of 390°C was supplied to the upper stage of the first-stage dehydration reactor. The residence time of the vaporized lactic acid feedstream inside the first-stage dehydration reactor was 0.1 seconds. At this time, the temperature drop in the first-stage dehydration reactor was approximately 13.6°C, and the discharge temperature from the first-stage dehydration reactor was 376.4°C.

[0101] The stream that had reacted in the first-stage dehydration reactor was transferred to the second-stage dehydration reactor via a transfer line. At this time, the temperature of the stream immediately discharged from the first-stage dehydration reactor was 376.4°C. Therefore, the stream discharged from the first-stage dehydration reactor was heated in a transfer line connected to the lower part of the first-stage dehydration reactor so that its temperature reached 390°C when it was introduced into the second-stage dehydration reactor.

[0102] At this time, the residence time of the stream transferred from the first-stage dehydration reactor inside the second-stage dehydration reactor was 1.4 seconds. Therefore, the value of Equation 2 was 0.07.

[0103] The dehydrated product stream from the second-stage dehydration reactor was discharged through the discharge line at a temperature of 349.4°C.

[0104] Similarly, the product stream after the reaction was completed was collected in the lower stage of the second-stage dehydration reactor and quantitatively analyzed by HPLC to calculate the acrylic acid yield and lactate conversion rate. The HPLC analysis method and the method for determining the acrylic acid yield and lactate conversion rate were the same as in Example 1.

[0105] [Comparative Example 2] The two-stage dehydration reactors for the dehydration reaction were both fixed-bed reactors, each packed with a dehydration catalyst. The first-stage dehydration reactor had a length of 2.5 m and an inner diameter of 4 m. The second-stage dehydration reactor had a length of 0.5 m and an inner diameter of 4 m. Therefore, the value of Equation 1 was 0.83. Hastelloy material was used for both the first and second-stage dehydration reactors. In addition, the dehydration catalyst was packed into both the first and second-stage dehydration reactors.

[0106] The upper section of the first-stage dehydration reactor was equipped with a feedstream supply unit, through which vaporized lactic acid molecules were supplied. A transfer line was provided between the first-stage and second-stage dehydration reactors, and a temperature controller maintained the temperature at 390°C. A shell-and-tube type heat exchanger was used as the temperature controller. In addition, a discharge line was provided in the lower section of the second-stage dehydration reactor to discharge the reaction product after the dehydration reaction.

[0107] As the dehydration catalyst, a calcium phosphate-based catalyst in the form of a composite phase consisting of Ca2P2O7 and Ca5(PO4)3(OH), formed into cylindrical pellets approximately 3 mm in diameter and 3 mm in length, was used. At this time, the mixed weight ratio of Ca2P2O7 to Ca5(PO4)3(OH) was 7:3.

[0108] A vaporized lactic acid feedstream at a temperature of 390°C was supplied to the upper stage of the first-stage dehydration reactor. The residence time of the vaporized lactic acid feedstream inside the first-stage dehydration reactor was 1.3 seconds. At this time, the temperature drop in the first-stage dehydration reactor was approximately 44.3°C, and the discharge temperature from the first-stage dehydration reactor was 345.7°C.

[0109] The stream that had reacted in the first-stage dehydration reactor was transferred to the second-stage dehydration reactor via a transfer line. At this time, the temperature of the stream immediately discharged from the first-stage dehydration reactor was 345.7°C. Therefore, the stream discharged from the first-stage dehydration reactor was heated in a transfer line connected to the lower part of the first-stage dehydration reactor so that its temperature when introduced into the second-stage dehydration reactor was 390°C.

[0110] At this time, the residence time of the stream transferred from the first-stage dehydration reactor inside the second-stage dehydration reactor was 0.24 seconds. Therefore, the value of Equation 2 was 0.84.

[0111] The dehydrated product stream from the second-stage dehydration reactor was discharged through the discharge line at a temperature of 380.5°C.

[0112] Similarly, the product stream after the reaction was completed was collected in the lower stage of the second-stage dehydration reactor and quantitatively analyzed by HPLC to calculate the acrylic acid yield and lactate conversion rate. The HPLC analysis method and the method for determining the acrylic acid yield and lactate conversion rate were the same as in Example 1.

[0113] The reaction conditions for Example 1 and Comparative Examples 1 and 2, as well as the yield of acrylic acid and the lactic acid conversion rate obtained from the reaction, are shown in Table 1 below. [Table 1]

[0114] The experimental results showed that in the examples satisfying Equation 1 of this disclosure, the target yield of 53 mol% or more was achieved. However, in the comparative examples that did not satisfy this condition, the yield was found to be less than 53 mol%.

[0115] Experimental Example 2 Using the simulation programs Aspen Plus V11 and gPROCESS 2022.1.0, the acrylic acid yield (mol%) based on the value of Equation 1 (L1 / (L1+L2)) was simulated, and the results are shown in Table 2 and Figure 2 below.

[0116] The dehydration reaction conditions for the simulation program were entered based on a two-stage reactor configuration, referencing Experimental Example 1. [Table 2]

[0117] Referring to Table 2 and Figure 2, we can confirm that the acrylic acid yield is expressed as a quadratic function with a negative coefficient in the highest-order term. We can also confirm that in order to achieve the target acrylic acid yield of 53 mol% or more in this invention, the value of L must satisfy 0.3 to 0.6.

Claims

1. In a two-stage reactor for lactate dehydration reactions, A feed supply unit to which lactic acid gas is supplied, A first-stage dehydration reactor filled with a catalyst for the lactate dehydration reaction, It includes a second-stage dehydration reactor packed with a catalyst for lactic acid dehydration, An apparatus for producing acrylic acid that satisfies the following equation 1. [Math 1] In the above formula 1, L １ L is the length of the first stage dehydration reactor. ２ is the length of the second stage dehydration reactor.

2. The acrylic acid production apparatus according to claim 1, wherein the yield of acrylic acid obtained by the acrylic acid production apparatus is 53 mol% or more.

3. The apparatus for producing acrylic acid according to claim 1, wherein the first-stage dehydration reactor and the second-stage dehydration reactor are connected by a transfer line, and the transfer line further includes a heating section.

4. In the first stage, a feedstream containing lactic acid gas molecules is supplied from the feed supply section to the upper stage of the first-stage dehydration reactor, which is filled with catalyst, and after the dehydration reaction proceeds, the stream is discharged from the lower stage. The process includes a second stage in which the stream discharged from the lower stage of the first stage dehydration reactor is supplied to the upper stage of the second stage dehydration reactor, which is filled with a catalyst, the dehydration reaction is carried out, and then the stream is discharged from the lower stage. The following equation 2 is satisfied: A method for producing acrylic acid. [Math 2] In the above formula 2, T １ T is the average time the feedstream remains in the first-stage dehydration reactor. ２ This is the average time that the stream supplied to the second-stage dehydration reactor remains in the second-stage dehydration reactor.

5. The method for producing acrylic acid according to claim 4, wherein the acrylic acid yield is 53 mol% or more.

6. The method for producing acrylic acid according to claim 4, wherein the stream discharged from the lower stage of the first-stage dehydration reactor is transferred to the second-stage dehydration reactor through a transfer line, and the temperature of the stream is maintained at 370°C or higher and 410°C or lower during the transfer.

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