Method for vaporizing lactic acid and method for producing acrylic acid from lactic acid

Abstract

The present disclosure relates to a method and apparatus for vaporizing lactic acid, and a method for preparing acrylic acid from lactic acid. According to the method and the device disclosed by the invention, the content of lactic acid oligomer can be reduced in a short time period, and the content of single-molecule lactic acid can be increased.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0008967 filed in the Korean Intellectual Property Office on January 20, 2023, and Korean Patent Application No. 10-2024-0008689 filed in the Korean Intellectual Property Office on January 19, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0003] The present disclosure relates to a method for vaporizing lactic acid and a method for producing acrylic acid from lactic acid. Background Art

[0004] Lactic acid, also called milk acid or lactate, is an organic acid having a relatively simple structure including both a hydroxyl group and a carboxyl group in a molecule.

[0005] Traditionally, lactic acid is naturally produced during the fermentation process of lactose, glucose, etc., and plays a role in improving the flavor of fermented foods and is non-toxic to the human body. Therefore, lactic acid has been widely used in the food field, such as flavoring agents, preservatives, and pH adjusters; in the cosmetic field, such as moisturizers and skin whitening agents; or in the medical field, such as intravenous solutions, dialysis solutions, and calcium agents.

[0006] Poly(lactic acid) or polylactide is biodegradable and has therefore recently attracted increasing attention as an eco-friendly alternative polymer capable of replacing naturally non-degradable plastics such as polyolefins, polystyrene and polyester produced from petroleum. In addition, it has received great attention as a precursor of acrylic acid, which is considered to be very important industrially.

[0007] Lactic acid can be mainly produced by microbial fermentation or chemical synthesis. Recently, a method for producing lactic acid using biomass resources such as starch-based biomass including corn, sugar-based biomass including sugarcane, or cellulose-based biomass obtained from woody plants or herbaceous plants as raw materials is being studied.

[0008] The lactic acid obtained in this way is usually concentrated and stored at a high concentration during storage and distribution after production. However, due to the structural characteristics peculiar to the lactic acid molecule containing both a hydroxyl group and a carboxyl group in the molecule, lactic acid usually forms a dimer structure or forms a dehydrated and condensed oligomer in which water molecules are removed.

[0009] Due to this dimerization or oligomerization, a large amount of lactic acid is lost. Oligomeric lactic acid has problems of increasing the amount of by-products produced in a chemical reaction using lactic acid and forming coke during the reaction process, thereby greatly reducing the efficiency of the reaction.

[0010] Therefore, when the concentrated and stored lactic acid is used as lactic acid itself or added to other chemical reactions, the content of lactic acid oligomers must be reduced. It is known that the chemical equilibrium between lactic acid and lactic acid oligomers only involves the concentration of lactic acid (i.e., the relative content ratio of lactic acid to water) and temperature. Since the equilibrium moves very slowly, interest in pretreatment methods using concentrated lactic acid (i.e., methods for reducing the content of lactic acid oligomers in the feed and increasing the content of single-molecule lactic acid) is increasing. Summary of the invention

[0011] Technical issues

[0012] In the present disclosure, a method of vaporizing lactic acid that can reduce the content of lactic acid oligomers and increase the content of single molecule lactic acid in a short period of time is provided.

[0013] Furthermore, a process for preparing acrylic acid from vaporized lactic acid is provided.

[0014] Technical Solution

[0015] In the present disclosure, a method for vaporizing lactic acid is provided, the method comprising the following steps: mixing and spraying a first flow of a liquid phase comprising an aqueous solution of lactic acid and a second flow of a gas phase comprising lactic acid vapor; vaporizing the aqueous solution of lactic acid by heat exchange between the first flow and the second flow; and obtaining a third flow of a gas phase comprising single-molecule lactic acid.

[0016] According to one embodiment of the present disclosure, the aqueous lactic acid solution contained in the first stream can be concentrated to a high lactic acid concentration of about 20 wt % to about 99 wt %, preferably about 20 wt % or greater, about 25 wt % or greater, about 30 wt % or greater, or about 35 wt % or greater, and about 99 wt % or less, about 95 wt % or less, about 90 wt % or less, or about 85 wt % or less.

[0017] In addition, the lactic acid polymer concentration (i.e., the concentration of lactic acid oligomers of lactic acid dimers, trimers or higher polymers) of the lactic acid aqueous solution contained in the first stream can be about 2 weight % to about 80 weight %, preferably about 2 weight % or greater, about 5 weight % or greater, about 7 weight % or greater, or about 8 weight % or greater, and about 80 weight % or less, about 70 weight % or less, about 60 weight % or less, about 55 weight % or less, about 40 weight % or less, or about 20 weight % or less, which indicates that the content of polymers is relatively high.

[0018] According to another embodiment of the present disclosure, the temperature of the first stream can be about 10°C to about 200°C, preferably about 10°C or higher, about 15°C or higher, or about 50°C or higher, and about 200°C or lower, about 180°C or lower, or about 150°C or lower.

[0019] According to one embodiment of the present disclosure, the lactic acid concentration of the lactic acid vapor contained in the second stream can be about 20 wt % to about 80 wt %, preferably about 20 wt % or greater, about 25 wt % or greater, about 30 wt % or greater, or about 35 wt % or greater, and about 80 wt % or less, about 70 wt % or less, about 60 wt % or less, about 55 wt % or less, about 50 wt % or less, or about 45 wt % or less.

[0020] Furthermore, the temperature of the second stream may be about 250°C to about 400°C, preferably about 250°C or higher, about 270°C or higher, or about 300°C or higher, and about 400°C or lower, about 380°C or lower, or about 360°C or lower.

[0021] Furthermore, in the mixing and spraying step, the flow rate of the first stream:the flow rate of the second stream may preferably be about 1:2 to about 1:25.

[0022] According to one embodiment of the present disclosure, at least a portion of the obtained third stream may be divided into the second stream and recycled into the second stream.

[0023] At the same time, an apparatus for vaporizing lactic acid is provided, the apparatus comprising: a feed supply part configured to supply a first flow containing an aqueous lactic acid solution; a lactic acid vapor supply part configured to supply a second flow containing lactic acid vapor; an injection part configured to mix and inject the lactic acid aqueous solution supplied from the feed supply part and the lactic acid vapor supplied from the lactic acid vapor supply part; a vaporization reaction part configured to vaporize the lactic acid aqueous solution after mixing and injecting; and an obtaining part configured to obtain a third flow containing vaporized lactic acid molecules.

[0024] At this time, the spraying part may include a first nozzle through which the lactic acid aqueous solution is sprayed and a second nozzle through which the lactic acid vapor is sprayed, and simultaneously mix and spray the lactic acid aqueous solution droplets and the lactic acid vapor.

[0025] Meanwhile, a method for preparing acrylic acid is provided, the method comprising the steps of: obtaining lactic acid molecules by vaporizing lactic acid according to any one of the above methods; subjecting the lactic acid molecules to a dehydration reaction to prepare acrylic acid; and obtaining acrylic acid.

[0026] In the present disclosure, the terms “first”, “second”, etc. are used to describe a plurality of components, and these terms are used only to distinguish a certain component from other components.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] Unless the context clearly indicates otherwise, the singular forms are intended to include the plural forms as well.

[0029] It will be further understood that the terms "include", "have" or "have" when used in this specification indicate the presence of stated features, numbers, steps, components, or a combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, components, or a combination thereof.

[0030] Furthermore, as used herein, when a layer or an element is referred to as being formed “on” a layer or an element, the layer or element may be directly formed on the layer or element, or other layers or elements may be additionally formed between layers, on an object, or on a substrate.

[0031] Since the present invention can be variously modified and has various forms, its specific embodiments are shown by way of example and will be described in detail. However, it is not intended to limit the present invention to the specific forms disclosed, but it should be understood that the present invention includes all modifications, equivalents and alternatives within the concept and technical scope of the present invention.

[0032] In the present disclosure, lactic acid is a compound represented by the following chemical formula, and is used to encompass all lactic acid isomers, naturally occurring lactic acid dimers, and lactic acid oligomers unless otherwise specified herein.

[0033]

[0034] Hereinafter, the present disclosure will be described in detail.

[0035] According to one aspect of the present disclosure, a method for vaporizing lactic acid is provided, the method comprising the following steps: mixing and spraying a first flow of a liquid phase comprising an aqueous solution of lactic acid and a second flow of a gas phase comprising lactic acid vapor; vaporizing the aqueous solution of lactic acid by heat exchange between the first flow and the second flow; and obtaining a third flow of a gas phase comprising single-molecule lactic acid.

[0036] The present inventors have found that when a highly concentrated aqueous lactic acid solution is mixed with high-temperature lactic acid vapor and sprayed, and vaporized by direct heat exchange, lactic acid can be efficiently vaporized in a very short period of time without increasing the oligomer concentration of lactic acid, thereby completing the present invention.

[0037] Lactic acid is widely used in the production of acrylic acid. When producing acrylic acid by dehydrating lactic acid, it is necessary to vaporize the lactic acid into lactic acid molecules because it proceeds through a gas phase reaction.

[0038] However, as mentioned above, lactic acid is usually concentrated and stored at a high concentration during storage or distribution after production. Due to the structural characteristics peculiar to the lactic acid molecule containing both hydroxyl and carboxyl groups in the molecule, lactic acid usually forms a dimer structure, or forms a dehydrated and condensed oligomer in which water molecules are removed.

[0039] These lactic acid oligomer molecules are carbonized during the vaporization or reaction step to form coke, which may reduce the active area of ​​the reaction catalyst and may also be included in the final product as a by-product. Most importantly, due to the presence of lactic acid oligomers, the content of lactic acid in the form of single molecules that can participate in the reaction is greatly reduced. Therefore, the lactic acid oligomers in the concentrated lactic acid aqueous solution must be converted into single molecules, thereby reducing the oligomer content and increasing the content of single-molecule lactic acid.

[0040] However, when the concentration is diluted by simply adding water to a concentrated aqueous lactic acid solution containing a high content of lactic acid oligomers, the equilibrium moves very slowly, and thus, it takes a very long time to reduce the content of lactic acid oligomers.

[0041] Usually, in order to shorten this time, a lactic acid aqueous solution having a high concentration of about 80 wt % or more is heated and vaporized. However, the vaporization efficiency of lactic acid is lower than that of water, so that water is vaporized first, and then the proportion of lactic acid in the gas phase decreases below about 20 wt %. In this case, since water evaporates first, the concentration of the remaining lactic acid aqueous solution further increases. Therefore, the concentration of oligomers in the remaining lactic acid aqueous solution also increases, which requires additional processing.

[0042] A method for vaporizing lactic acid according to one aspect of the present disclosure comprises the following steps: mixing and spraying a first stream of a liquid phase comprising an aqueous solution of lactic acid and a second stream of a gas phase comprising lactic acid vapor; vaporizing the aqueous solution of lactic acid by heat exchange between the first stream and the second stream; and obtaining a third stream of a gas phase comprising single-molecule lactic acid.

[0043] That is, according to one embodiment of the present disclosure, instead of directly heating and vaporizing the high-concentration lactic acid aqueous solution, the high-concentration lactic acid aqueous solution is sprayed in the form of an aerosol (or droplets), and the high-temperature lactic acid vapor is mixed therewith and sprayed. Therefore, the lactic acid is vaporized by rapid heat exchange between the high-concentration lactic acid droplets sprayed in the form of an aerosol and the lactic acid vapor, so that vaporized single-molecule lactic acid can be obtained.

[0044] In addition, the concentration of lactic acid in the third stream can be about 60 wt % or less, about 55 wt % or less, or about 50 wt % or less. Depending on process conditions, the lower limit may not be significant and is about 0.1 wt % or greater, or about 5 wt % or greater.

[0045] According to one embodiment of the present disclosure, the aqueous lactic acid solution contained in the first stream can be concentrated to a high lactic acid concentration of about 20 wt % to about 99 wt %, preferably about 20 wt % or greater, about 25 wt % or greater, about 30 wt % or greater, or about 35 wt % or greater, and about 99 wt % or less, about 95 wt % or less, about 90 wt % or less, or about 85 wt % or less.

[0046] In addition, the lactic acid polymer concentration (i.e., the concentration of lactic acid oligomers of lactic acid dimers, trimers or higher polymers) of the lactic acid aqueous solution contained in the first stream can be about 2 weight % to about 80 weight %, preferably about 2 weight % or greater, about 5 weight % or greater, about 7 weight % or greater, or about 8 weight % or greater, and about 80 weight % or less, about 70 weight % or less, about 60 weight % or less, about 55 weight % or less, about 40 weight % or less, or about 20 weight % or less, which indicates that the content of polymers is relatively high.

[0047] Herein, the aqueous lactic acid solution contained in the first stream (i.e., the lactic acid feed in the process) is in a state where lactic acid is dissolved in water, and as described above, naturally includes all single-molecule lactic acid, lactic acid dimers, and lactic acid oligomers according to temperature and concentration conditions. The lactic acid concentration described herein also refers to the concentration of lactic acid-based compounds including not only single-molecule lactic acid, but also single-molecule lactic acid, lactic acid dimers, and lactic acid oligomers.

[0048] More specifically, for example, when the known oligomerization equilibrium constant based on lactic acid is calculated by computer modeling, the oligomer content of the total lactic acid-based compound for each concentration is shown in Table 1 below.

[0049] However, this may have a slight calculation error depending on the actual calculation model, and the actual measured value may also have a slight measurement error depending on the measurement conditions or the measurement method (titration or HPLC).

[0050] [Table 1]

[0051]

[0052] Furthermore, the aqueous lactic acid solution supplied by the feed may be subjected to a heating process.

[0053] According to another embodiment of the present disclosure, the temperature of the first stream can be about 10°C to about 200°C, preferably about 10°C or higher, about 15°C or higher, or about 50°C or higher, and about 200°C or lower, about 180°C or lower, or about 150°C or lower.

[0054] When the temperature of the first stream is too low outside the above temperature range, there may be a problem that lactic acid is not sufficiently vaporized due to the low temperature of the mixture. When the temperature is too high, there may be a problem that the pressure becomes too high to maintain the temperature.

[0055] The lactic acid aqueous solution supplied by the feed is heated and then sprayed into the vaporization reactor in the form of droplets via a transfer line and a nozzle. The temperature of the lactic acid aqueous solution is kept high, and due to the high pressure, it is more conducive to obtaining small-sized droplets.

[0056] At this time, separately from the first stream, a second stream containing lactic acid vapor is additionally mixed with the first stream in the form of droplets and injected into the vaporization reactor through a transfer line and a nozzle.

[0057] When mixing and spraying, the delivery lines of the first and second streams can be first merged before spraying, and then mixed and sprayed through the same nozzle. On the contrary, it is more preferred that the first and second streams are mixed and sprayed into the vaporization reactor through separate nozzles.

[0058] The second stream immediately reduces the concentration of lactic acid in the first stream comprising highly concentrated lactic acid and simultaneously transfers heat energy to the first stream to promote vaporization of lactic acid molecules, thereby reducing the ratio of oligomers.

[0059] When water vapor is used as a medium to transfer heat to lactic acid, a large amount of water vapor must be used to heat the lactic acid to a desired temperature, and thus there is a problem in that the concentration of lactic acid in the vaporization product, ie, vaporized lactic acid vapor, decreases.

[0060] Furthermore, the temperature of the second stream may be about 250°C to about 400°C, preferably about 250°C or higher, about 270°C or higher, or about 300°C or higher, and about 400°C or lower, about 380°C or lower, or about 360°C or lower.

[0061] When the temperature of the second stream is too low outside the above range, lactic acid may not be sufficiently vaporized due to the low temperature of the mixture, and lactic acid vapor may condense into liquid. When the temperature of the second stream is too high outside the above range, the pressure may become too high to maintain the temperature, and there may be a problem that lactic acid in the lactic acid vapor is thermally decomposed.

[0062] When the injection amount and injection rate of the first stream are too low, the flow rate of lactic acid supplied may become too low, causing a problem of overreaction in the subsequent dehydration reaction, while when they are too high, a large amount of heat is required for vaporization, resulting in incomplete vaporization.

[0063] When the injection amount and injection rate of the second stream are too low, incomplete vaporization may occur due to reduced heat supplied for vaporization, and when they are too high, the concentration of lactic acid may be diluted, which may cause problems in the subsequent product separation process.

[0064] At this time, in the mixing and spraying step, the flow rate of the first stream: the flow rate of the second stream may preferably be about 1:2 to about 1:25.

[0065] When the flow rate of the first stream is too low outside the above range, the flow rate of the supplied lactic acid becomes low, which may lead to lower efficiency and increased load during the product separation process. When the flow rate of the second stream is too low, the heat supplied for vaporization may be reduced, and incomplete vaporization may occur.

[0066] According to another embodiment of the present disclosure, before the first stream and the second stream are mixed and sprayed into the vaporization reactor in the form of droplets via a transfer line and a nozzle, the interior of the vaporization reactor is preferably pre-saturated with lactic acid vapor.

[0067] When the first stream is injected into the reactor under high temperature conditions in this manner, it is possible to prevent the phenomenon that water evaporates first and lactic acid concentrates in droplets of the first stream injected instantaneously under high temperature conditions.

[0068] At this time, it may be desirable to perform the reaction in the vaporization reactor while maintaining a temperature of about 150°C to about 350°C.

[0069] At the same time, an apparatus for vaporizing lactic acid is provided, the apparatus comprising: a feed supply part configured to supply a first flow containing an aqueous lactic acid solution; a lactic acid vapor supply part configured to supply a second flow containing lactic acid vapor; an injection part configured to mix and inject the lactic acid aqueous solution supplied by the feed supply part and the lactic acid vapor supplied by the lactic acid vapor supply part; a vaporization reaction part configured to vaporize the lactic acid aqueous solution after mixing and injecting; and an obtaining part configured to obtain a third flow containing vaporized lactic acid molecules.

[0070] At this time, the spraying part may include a first nozzle through which the lactic acid aqueous solution is sprayed and a second nozzle through which the lactic acid vapor is sprayed, and simultaneously mix and spray the lactic acid aqueous solution droplets with the lactic acid vapor.

[0071] Meanwhile, a method for preparing acrylic acid is provided, the method comprising the steps of: obtaining lactic acid molecules by vaporizing lactic acid according to the above method; subjecting the lactic acid molecules to a dehydration reaction to prepare acrylic acid; and obtaining acrylic acid.

[0072] The reaction for producing acrylic acid by intramolecular dehydration of lactic acid can be represented by the following chemical formula, and is known to proceed in one step in the presence of a catalyst.

[0073]

[0074] However, in the case of a method for preparing acrylic acid according to one aspect of the present disclosure, in addition to the above-mentioned contents related to the vaporization of lactic acid, the method for preparing acrylic acid from vaporized lactic acid may also adopt catalysts, reactors, or reaction conditions generally known in the technical field of the present invention.

[0075] For example, the catalyst for the dehydration reaction of lactic acid can be CaSO4 / Na2SO4; Na4P2O7 / CaSO4; Na4P2O7 / Ca3(PO4)2; NaH2PO4-NaHCO3 / SiO2; AlPO4-NH3; Ca3(PO4)2 / CaSO4; and the like.

[0076] The dehydration reaction using a solid catalyst can be performed as a continuous reaction using a fixed reactor, as a batch reaction, etc. When a fixed reactor is used, a product can be produced continuously by loading the reactor with a solid catalyst and continuously supplying reactants to the reactor for the reaction.

[0077] The temperature of the dehydration reaction may be about 300° C. to about 500° C., or about 300° C. to about 400° C. The reaction pressure may be about 1 atmosphere to about 5 atmospheres, or about 1 atmosphere to about 2 atmospheres.

[0078] The feed rate of the reactants may vary depending on the type of reactor, other reaction conditions, etc. Specifically, for example, the gas phase lactic acid feed rate (weight hourly space velocity, WHSV) may be about 0.05 / hour to about 1.0 / hour, or about 0.10 / hour to about 0.50 / hour.

[0079] When the above conditions are not satisfied, a decomposition reaction due to oligomerization or hydrogenation may proceed, which may cause problems such as a decrease in reaction efficiency or a decrease in conversion rate.

[0080] Beneficial Effects

[0081] According to the method and apparatus for vaporizing lactic acid according to one aspect of the present disclosure, it is possible to reduce the content of lactic acid oligomers and increase the content of single molecule lactic acid in a high concentration lactic acid aqueous solution within a short period of time. DETAILED DESCRIPTION

[0082] Hereinafter, the action and effect of the present invention will be described in more detail with reference to specific embodiments of the present invention. However, these embodiments are presented for illustrative purposes only, and the scope of the present invention is not limited thereby in any way.

[0083] <Example>

[0084] The lactic acid feed solution to be used as the first stream and the heat transfer medium to be used as the second stream were prepared under the conditions summarized in Table 2 below.

[0085] [Table 2]

[0086]

[0087] *Compared to 100 wt% of the flow rate of the aqueous lactic acid solution supplied as the first flow

[0088] In addition, an apparatus for vaporizing lactic acid is prepared that includes: a feed supply portion configured to supply a first flow containing an aqueous lactic acid solution; a lactic acid vapor supply portion configured to supply a second flow containing lactic acid vapor; an injection portion configured to mix the lactic acid aqueous solution supplied by the feed supply portion and the lactic acid vapor supplied by the lactic acid vapor supply portion and to inject through each nozzle; a vaporization reaction portion configured to vaporize the lactic acid aqueous solution after mixing and injecting; and an obtaining portion configured to obtain a third flow containing vaporized lactic acid molecules.

[0089] Thermometers and temperature control devices are provided in the feed supply section and the vapor supply section, whereby the temperatures of the supplied feed (first stream) and lactic acid vapor (second stream) can be adjusted. The obtaining section is equipped with a thermometer to measure the temperature of the third stream.

[0090] First, lactic acid vapor is introduced into a vaporization reactor so that the interior of the vaporization reactor is saturated with the lactic acid vapor.

[0091] Thereafter, the lactic acid aqueous solution is supplied to the first stream through the feed supply part, the lactic acid vapor is supplied through the lactic acid vapor supply part, and they are continuously mixed and sprayed into the interior of the vaporization reaction part through each nozzle. Thus, the third stream containing vaporized lactic acid molecules is obtained through the obtaining part.

[0092] A portion of the third stream is divided into the second stream and fed back to the second stream, and the unvaporized feed is fed back to the first stream.

[0093] The obtained third stream was analyzed; and the concentration of the total lactic acid-based compound in the third stream and the ratio of the oligomer therein were measured and calculated, which are summarized in the following table.

[0094] In Comparative Examples 1 and 2, a vaporization method of heating the vaporization reaction portion was used without using a separate heat transfer medium.

[0095] [Table 3]

[0096]

[0097] Referring to the above table, it can be clearly determined that one embodiment of the present disclosure can provide lactic acid vapor having a high concentration by continuously vaporizing lactic acid while relatively reducing the content of lactic acid oligomers in the resulting product.

[0098] In the case of general heating, it is found that the temperature of the generated lactic acid vapor is low, the concentration of the lactic acid vapor is low, and the ratio of oligomers is relatively high despite the low temperature. In addition, when steam is used, the temperature of the generated lactic acid vapor increases, but there is a problem that the ratio of oligomers is relatively high despite the low concentration of the lactic acid vapor.

Claims

1. A method for vaporizing lactic acid, The following steps are involved: mixing and spraying a first stream of a liquid phase comprising an aqueous lactic acid solution and a second stream of a gas phase comprising lactic acid vapor; vaporizing the aqueous lactic acid solution by heat exchange between the first stream and the second stream; as well as A third stream of a gas phase comprising unimolecular lactic acid is obtained.

2. The method for vaporizing lactic acid according to claim 1, The lactic acid concentration of the lactic acid aqueous solution contained in the first flow is 20 wt % to 99 wt %.

3. The method for vaporizing lactic acid according to claim 1, The lactic acid polymer concentration of the lactic acid aqueous solution contained in the first flow is 2 wt % to 80 wt %.

4. The method for vaporizing lactic acid according to claim 1, The temperature of the first stream is 10°C to 200°C.

5. The method for vaporizing lactic acid according to claim 1, The lactic acid concentration of the lactic acid vapor contained in the second stream is 20 wt % to 80 wt %.

6. The method for vaporizing lactic acid according to claim 1, The temperature of the second flow is 250°C to 400°C.

7. The method for vaporizing lactic acid according to claim 1, Wherein in the mixing and spraying step, the ratio of the flow rate of the first stream to the flow rate of the second stream is 1:2 to 1:

25.

8. The method for vaporizing lactic acid according to claim 1, At least a portion of the third stream is divided into the second stream and recycled into the second stream.

9. A method for preparing acrylic acid, The following steps are involved: Obtaining lactic acid molecules by vaporizing lactic acid according to the method of any one of claims 1 to 8; subjecting the lactic acid molecules to a dehydration reaction to produce acrylic acid; and The acrylic acid is obtained.

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