Lactic acid vaporization method and acrylic acid production method

Abstract

The present specification relates to a method for vaporizing lactic acid, a lactic acid vaporization apparatus, and a method for producing acrylic acid from lactic acid. The method and apparatus for vaporizing lactic acid of the present invention can reduce the content of lactic acid oligomers and increase the content of lactic acid monomolecules in a short period of time.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0008967, filed January 20, 2023, and Korean Patent Application No. 10-2024-0008689, filed January 19, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present specification relates to a method for vaporizing lactic acid and a method for producing acrylic acid from lactic acid. [Background technology]

[0003] Lactic acid, also known as lactose, is an organic acid with a relatively simple structure that contains both hydroxyl and carboxyl groups within the molecule.

[0004] Lactic acid has traditionally been produced naturally during the fermentation process of lactose and glucose, and has the role of improving the flavor of fermented foods. It is non-toxic to the human body and has been used in a variety of applications in the food industry, such as as a flavoring agent, preservative, and pH adjuster; in the beauty industry, such as as a moisturizer and skin whitening agent; and in the medical industry, such as in intravenous fluids, dialysis fluids, and calcium supplements.

[0005] Recently, lactic acid polymers, or polylactides, have been attracting increasing attention as biodegradable environmentally friendly polymers that can replace non-biodegradable plastics such as petroleum-derived polyolefins, polystyrene, and polyesters. They are also attracting considerable attention as precursors to acrylic acid, which is considered to be of great industrial importance.

[0006] Lactic acid can be produced mainly by microbial fermentation or chemical synthesis, but recently research has been conducted into methods for producing lactic acid using biomass resources as raw materials, such as starch-based biomass such as corn, sugar-based biomass such as sugarcane, or cellulosic biomass obtained from woody or herbaceous plants.

[0007] Lactic acid obtained in this way is usually stored in a highly concentrated state during storage and distribution after production. However, due to the structural characteristics unique to lactic acid molecules, which contain both hydroxyl and carboxyl groups in the molecule, it often forms a dimer structure or an oligomer in the form of dehydration condensation due to the removal of water molecules.

[0008] A large amount of lactic acid is lost due to such dimerization or oligomerization, and the oligomerized lactic acid increases the amount of by-products generated in chemical reactions using lactic acid and forms coking during the reaction, significantly reducing the efficiency of the reaction.

[0009] Therefore, when concentrated and stored lactic acid is used as lactic acid itself or introduced into other chemical reactions, it is necessary to reduce the content of lactic acid oligomers. However, it is known that the chemical equilibrium between lactic acid and lactic acid oligomers is related only to the concentration of lactic acid, i.e., the relative content ratio of lactic acid to water, and temperature, and the equilibrium shift rate is very slow. Therefore, there has been growing interest in pretreatment methods for using concentrated lactic acid, i.e., methods for reducing the content of lactic acid oligomers and increasing the content of monomolecular lactic acid in the feed. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a method for vaporizing lactic acid, which can reduce the content of lactic acid oligomers and increase the content of lactic acid monomolecules in a short period of time.

[0011] The present specification also provides a method for producing acrylic acid from the vaporized lactic acid. [Means for solving the problem]

[0012] The present specification provides a method for vaporizing lactic acid, which includes the steps of: mixing and spraying a first stream in a liquid phase containing an aqueous lactic acid solution and a second stream in a gas phase containing lactic acid vapor; vaporizing the aqueous lactic acid solution by heat exchange between the first stream and the second stream; and obtaining a third stream in a gas phase containing lactic acid monomers.

[0013] According to one embodiment of the invention, the lactic acid aqueous solution contained in the first stream may have a lactic acid concentration of about 20 to about 99 wt%, or about 20 wt% or more, or about 25 wt% or more, or about 30 wt% or more, or about 35 wt% or more, or may be highly concentrated, such as about 99 wt% or less, about 95 wt% or less, about 90 wt% or less, or about 85 wt% or less.

[0014] The lactic acid aqueous solution contained in the first stream may have a lactic acid polymer concentration, i.e., a concentration of lactic acid dimers or lactic acid oligomers of trimers or higher, of about 2 to about 80 wt%, or about 2 wt% or more, or about 5% or more, or about 7 wt% or more, or about 8 wt% or more, or may have a relatively high polymer content of about 80 wt% or less, or about 70 wt% or less, or about 60 wt% or less, or about 55 wt% or less, or about 40 wt% or less, or about 20 wt% or less.

[0015] According to another embodiment of the invention, the temperature of the first stream may be about 10 to about 200°C, preferably about 10°C or more, or about 15°C or more, or about 50°C or more, and may be about 200°C or less, or about 180°C or less, or about 150°C or less.

[0016] According to one embodiment of the invention, the lactic acid vapor contained in the second stream may have a lactic acid concentration of about 20 to about 80 wt%, or greater than about 20 wt%, or greater than about 25 wt%, or greater than about 30 wt%, or greater than about 35 wt%, or less than about 80 wt%, or less than about 70 wt%, or less than about 60 wt%, or less than about 55 wt%, or less than about 50 wt%, or less than about 45 wt%.

[0017] The temperature of the second stream may be about 250 to about 400°C, preferably about 250°C or higher, or about 270°C or higher, or about 300°C or higher, and may be about 400°C or lower, or about 380°C or lower, or about 360°C or lower.

[0018] In the mixing and spraying step, the flow rate of the first stream: the flow rate of the second stream is preferably about 1:2 to about 1:25.

[0019] According to one embodiment of the invention, at least a portion of the resulting third stream can be branched off and reused as the second stream.

[0020] Meanwhile, the present specification provides a lactic acid vaporization device including: a feed supply unit that supplies a first stream containing an aqueous lactic acid solution; a lactic acid vapor supply unit that supplies a second stream containing lactic acid vapor; a spray unit that mixes and sprays the aqueous lactic acid solution transferred from the feed supply unit and the lactic acid vapor transferred from the lactic acid vapor supply unit; a vaporization reaction unit that vaporizes the mixed and sprayed aqueous lactic acid solution; and a harvesting unit that obtains a third stream containing vaporized lactic acid molecules.

[0021] In this case, the spray unit 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, so that the lactic acid aqueous solution droplets and the lactic acid vapor are simultaneously mixed and sprayed.

[0022] Meanwhile, the present specification provides a method for producing acrylic acid, including the steps of: vaporizing lactic acid by any one of the above methods to obtain lactic acid molecules; dehydrating the lactic acid molecules to produce acrylic acid; and obtaining the acrylic acid.

[0023] In the present invention, terms such as first and second are used to describe various components, and the terms are used only to distinguish one component from another.

[0024] Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention.

[0025] The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0026] As used herein, terms such as "comprises," "comprises," or "having" are intended to describe embodied features, numbers, steps, components, or combinations thereof, but do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

[0027] Furthermore, in this specification, when a layer or element is referred to as being formed "on" another layer or element, it means that the layer or element is formed directly on the other layer or element, or that other layers or elements can be additionally formed between the layers, on the object, or on the substrate.

[0028] Although the present invention can be embodied in various forms through various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the invention to the specific disclosed embodiments, and that the invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the invention.

[0029] In the present specification, lactic acid refers to a compound represented by the following chemical formula, and unless otherwise specified in the present specification, it is used as a concept that encompasses all lactic acid isomers, naturally occurring lactic acid dimers, and lactic acid oligomers. [ka]

[0030] The present invention will be described in detail below.

[0031] According to one aspect of the present invention, there is provided a method for vaporizing lactic acid, comprising the steps of: mixing and spraying a first stream in a liquid phase containing an aqueous lactic acid solution and a second stream in a gas phase containing lactic acid vapor; vaporizing the aqueous lactic acid solution by heat exchange between the first stream and the second stream; and obtaining a third stream in a gas phase containing lactic acid monomers.

[0032] The inventors of the present invention have found that when a highly concentrated aqueous lactic acid solution is mixed and sprayed with high-temperature lactic acid vapor and vaporized by direct heat exchange, lactic acid can be vaporized efficiently in a very short time without increasing the oligomer concentration of lactic acid, and have completed the present invention.

[0033] Lactic acid is often used in the production of acrylic acid, but when acrylic acid is produced by dehydrating lactic acid, the reaction is carried out in a gas phase, so it is necessary to vaporize the lactic acid into lactic acid molecules.

[0034] However, as mentioned above, lactic acid is usually stored in a highly concentrated state during storage and distribution after production. Due to the structural characteristics unique to lactic acid molecules, which contain both hydroxyl and carboxyl groups in the molecule, it often forms a dimer structure or an oligomer in the form of dehydration condensation due to the removal of water molecules.

[0035] Such lactic acid oligomer molecules can be carbonized during the vaporization or reaction stage to form coke, reducing the active area of ​​the reaction catalyst, and can also be contained as a by-product in the final product. Moreover, the presence of lactic acid oligomers significantly reduces the content of monomolecular lactic acid that can participate in the reaction. Therefore, it is necessary to convert the lactic acid oligomers into monomolecular forms in the concentrated lactic acid aqueous solution to reduce the content of oligomers and increase the content of monomolecular lactic acid.

[0036] However, when water is simply added to a concentrated aqueous lactic acid solution containing a high content of lactic acid oligomers to dilute the concentration, the equilibrium shift rate is very slow, so it takes a very long time to reduce the content of lactic acid oligomers.

[0037] Generally, to shorten this time, a high-concentration lactic acid aqueous solution of about 80 wt% or more is heated and vaporized, but because the vaporization efficiency of lactic acid is lower than that of water, water vaporizes first, and the proportion of lactic acid in the gas phase falls below about 20 wt%. In this case, as water vaporizes first, the concentration of the remaining lactic acid aqueous solution increases, which in turn increases the concentration of oligomers in the remaining lactic acid aqueous solution, necessitating an additional treatment process.

[0038] A method for vaporizing lactic acid according to one aspect of the present invention includes the steps of: mixing and spraying a first stream of a liquid phase containing an aqueous lactic acid solution and a second stream of a gas phase containing lactic acid vapor; vaporizing the aqueous lactic acid solution by heat exchange between the first stream and the second stream; and obtaining a third stream of a gas phase containing lactic acid monomers.

[0039] That is, according to one embodiment of the present invention, instead of directly heating and vaporizing a high-concentration lactic acid aqueous solution, a high-concentration lactic acid aqueous solution is sprayed in the form of an aerosol (or droplets) and mixed with high-temperature lactic acid vapor and sprayed therewith, whereby rapid heat exchange occurs between the high-concentration lactic acid droplets sprayed in the form of an aerosol and the lactic acid vapor, thereby vaporizing the lactic acid and obtaining vaporized lactic acid monomolecules.

[0040] The concentration of lactic acid in the third stream may be about 60 wt% or less, or about 55 wt% or less, or about 50 wt% or less, and the lower limit may be less significant depending on process conditions, but may be about 0.1 wt% or more, or about 5 wt% or more.

[0041] According to one embodiment of the invention, the lactic acid aqueous solution contained in the first stream may have a lactic acid concentration of about 20 to about 99 wt%, or about 20 wt% or more, or about 25 wt% or more, or about 30 wt% or more, or about 35 wt% or more, or may be highly concentrated, such as about 99 wt% or less, about 95 wt% or less, about 90 wt% or less, or about 85 wt% or less. The lactic acid aqueous solution contained in the first stream may have a lactic acid polymer concentration, i.e., a concentration of lactic acid dimers or lactic acid oligomers of trimers or higher, of about 2 to about 80 wt%, or about 2 wt% or more, or about 5% or more, or about 7 wt% or more, or about 8 wt% or more, or may have a relatively high polymer content of about 80 wt% or less, or about 70 wt% or less, or about 60 wt% or less, or about 55 wt% or less, or about 40 wt% or less, or about 20 wt% or less.

[0042] Here, the first stream, i.e., the aqueous lactic acid solution contained in the lactic acid feed in the process, is a state in which lactic acid is dissolved in water, and as described above, naturally means a state in which lactic acid monomolecules, lactic acid dimers, and lactic acid oligomers are all contained depending on the temperature and concentration conditions. The lactic acid concentration described here also means the concentration of lactic acid-based compounds including not only lactic acid monomolecules but also lactic acid monomolecules, lactic acid dimers, and lactic acid oligomers.

[0043] More specifically, for example, when calculated by computer modeling based on the known oligomerization equilibrium constant of lactic acid, the oligomer content for each concentration of the total lactic acid-based compounds is as shown in Table 1 below.

[0044] However, this may result in slight calculation errors depending on the actual calculation model, and the actual measured values ​​may also have slight measurement errors depending on the measurement conditions and measurement method (titration or HPLC). [Table 1]

[0045] The aqueous lactic acid solution supplied from the feed can then be subjected to a heating process.

[0046] According to another embodiment of the invention, the temperature of the first stream may be about 10 to about 200°C, preferably about 10°C or more, or about 15°C or more, or about 50°C or more, and may be about 200°C or less, or about 180°C or less, or about 150°C or less.

[0047] If the temperature of the first stream is too low beyond the temperature range, the temperature of the mixture is low and the lactic acid may not be sufficiently vaporized. If the temperature is too high, the pressure may become too high to maintain the temperature.

[0048] The aqueous lactic acid solution supplied from the feed is heated and then sprayed in the form of droplets into the vaporization reactor through a transfer line and a nozzle. Maintaining a high temperature of the aqueous lactic acid solution and a high pressure are advantageous for obtaining smaller droplets.

[0049] At this time, a second stream containing lactic acid vapor, separate from the first stream, is also mixed and sprayed in droplet form with the first stream into the vaporization reactor through a transfer line and a nozzle.

[0050] During mixed spraying, the transfer lines of the first and second streams may be joined together before spraying, and then mixed and sprayed through the same nozzle. However, it is more preferable that the first and second streams be mixed and sprayed into the gasification reactor through separate nozzles.

[0051] The second stream instantaneously reduces the concentration of lactic acid in the first stream containing highly concentrated lactic acid, and at the same time transfers thermal energy to the first stream to promote the vaporization of lactic acid molecules and reduce the proportion of oligomers.

[0052] When water vapor or the like is used as a medium for transferring heat to lactic acid, a large amount of water vapor must be used to heat lactic acid to a desired temperature, which results in a problem of a low lactic acid concentration in the vaporized product, i.e., vaporized lactic acid vapor.

[0053] The temperature of the second stream may be about 250 to about 400°C, preferably about 250°C or higher, or about 270°C or higher, or about 300°C or higher, and may be about 400°C or lower, or about 380°C or lower, or about 360°C or lower.

[0054] If the temperature of the second stream is excessively low beyond the above range, the lactic acid may not be sufficiently vaporized due to the low temperature of the mixture, and the lactic acid vapor may condense into a liquid. If the temperature of the second stream is excessively high beyond the above range, the pressure may become excessively high in order to maintain the temperature, and the lactic acid may be thermally decomposed in the lactic acid vapor.

[0055] If the spray amount and spray rate of the first stream are too low, the flow rate of lactic acid supplied will be too low, which may cause an over-reaction in the dehydration reaction proceeding to the next stage. If the spray amount and spray rate are too high, the heat required for vaporization will be too high, which may cause incomplete vaporization.

[0056] If the spray amount and spray rate of the second stream are too low, the heat supplied to the vaporization will be insufficient, which may result in incomplete vaporization. If they are too high, the concentration of lactic acid will decrease due to dilution, which may cause problems in the subsequent product separation process.

[0057] At this time, in the mixing and spraying step, the flow rate of the first stream: the flow rate of the second stream is preferably about 1:2 to about 1:25.

[0058] If the flow rate ratio of the first stream is too small beyond the above range, the flow rate of the supplied lactic acid will be reduced, resulting in low efficiency and a problem of increased load on the product separation process. If the flow rate ratio of the second stream is too small, the heat supplied to the vaporization will be reduced, resulting in incomplete vaporization.

[0059] According to another embodiment of the invention, before the first stream and the second stream are mixed and sprayed in the form of droplets into the vaporization reactor through a transfer line and a nozzle, respectively, the inside of the vaporization reactor is preferably saturated with lactic acid vapor in advance.

[0060] In this manner, when the first stream is sprayed into the reactor at high temperature, the water in the droplets of the first stream sprayed instantaneously at high temperature can be prevented from evaporating first, which can prevent the lactic acid in the droplets from concentrating.

[0061] At this time, it is preferable to allow the reaction to proceed in the vaporization reactor while maintaining a temperature condition of about 150 to about 350°C.

[0062] Meanwhile, the present specification provides a lactic acid vaporization device including: a feed supply unit that supplies a first stream containing an aqueous lactic acid solution; a lactic acid vapor supply unit that supplies a second stream containing lactic acid vapor; a spray unit that mixes and sprays the aqueous lactic acid solution transferred from the feed supply unit and the lactic acid vapor transferred from the lactic acid vapor supply unit; a vaporization reaction unit that vaporizes the mixed and sprayed aqueous lactic acid solution; and a harvesting unit that obtains a third stream containing vaporized lactic acid molecules.

[0063] In this case, the spray unit 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, so that the lactic acid aqueous solution droplets and the lactic acid vapor are simultaneously mixed and sprayed.

[0064] Meanwhile, the present specification provides a method for producing acrylic acid, comprising: a step of vaporizing lactic acid by any of the methods described above to obtain lactic acid molecules; a step of producing acrylic acid by dehydrating the lactic acid molecules; and a step of obtaining the acrylic acid.

[0065] The reaction of producing acrylic acid by dehydration of lactic acid molecules may be represented by the following chemical formula, and is known to occur in one step in the presence of a catalyst.

[0066] [ka]

[0067] However, in the case of the method for producing acrylic acid according to one aspect of the present invention, except for the content related to the vaporization of lactic acid described above, a catalyst, a reactor, reaction conditions, and the like generally known in the technical field to which the present invention pertains can be adopted in relation to the method for producing acrylic acid from vaporized lactic acid.

[0068] For example, catalysts used in the lactic acid dehydration reaction include CaSO4 / Na2SO4; Na4P2O7 / CaSO4; Na4P2O7 / Ca3(PO4)2; NaH2PO4-NaHCO3 / SiO2; AlPO4-NH3; and Ca3(PO4)2 / CaSO4.

[0069] The dehydration reaction using a solid catalyst may be carried out as a continuous reaction using a fixed reactor, a batch reaction, etc. When a fixed reactor is used, the reactor is filled with a solid catalyst, and reactants are continuously supplied to the reactor and reacted, thereby allowing the product to be continuously produced.

[0070] The temperature of the dehydration reaction may be about 300 to about 500° C., or about 300 to about 400° C. The reaction pressure may be about 1 to about 5 atmospheres, or about 1 to about 2 atmospheres.

[0071] The supply rate of the reactants may vary depending on the shape and type of the reactor, other reaction conditions, etc., but specifically, for example, the supply rate of lactic acid in the gas (Weight Hourly Space Velocity, WHSV) may be about 0.05 to about 1.0 / hr, or about 0.10 to about 0.50 / hr.

[0072] If the above conditions are exceeded, problems may occur such as a cracking reaction due to oligomerization or hydrogenation, resulting in a decrease in reaction efficiency or conversion rate. [Effects of the Invention]

[0073] According to the method and apparatus for vaporizing lactic acid according to one aspect of the present invention, the content of lactic acid oligomers can be reduced and the content of lactic acid monomolecules can be increased in a short period of time in a highly concentrated aqueous lactic acid solution. DETAILED DESCRIPTION OF THE INVENTION

[0074] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0075] <Example> The lactic acid feed solution used as the first stream and the heat transfer medium used as the second stream were prepared under the conditions summarized in Table 2 below. [Table 2]

[0076] A lactic acid vaporization apparatus was prepared, which included a feed supply unit that supplies a first stream containing the aqueous lactic acid solution; a lactic acid vapor supply unit that supplies a second stream containing lactic acid vapor; a spray unit in which the aqueous lactic acid solution transferred from the feed supply unit and the lactic acid vapor transferred from the lactic acid vapor supply unit are mixed and sprayed through their respective nozzles; a vaporization reaction unit in which the aqueous lactic acid solution after mixing and spraying is vaporized; and a harvesting unit that obtains a third stream containing vaporized lactic acid molecules.

[0077] The feed supply section and steam supply section were equipped with thermometers and temperature controllers to allow adjustment of the temperatures of the supplied feed (first stream) and lactic acid vapor (second stream), and the harvesting section was equipped with a thermometer to measure the temperature of the third stream.

[0078] First, lactic acid vapor was introduced into the vaporization reactor so that the inside of the vaporization reactor was saturated with lactic acid vapor.

[0079] Thereafter, the lactic acid aqueous solution was supplied as a first stream through the feed supply unit, and the lactic acid vapor was supplied through the lactic acid vapor supply unit. The lactic acid aqueous solution and the lactic acid vapor were continuously mixed and sprayed into the vaporization reaction unit through the respective nozzles, and a third stream containing vaporized lactic acid molecules was obtained through the collection unit.

[0080] A portion of the third stream was branched off and fed again as the second stream, and the unvaporized feed was fed again as the first stream.

[0081] The resulting third stream was analyzed, and the concentration of all lactic acid-based compounds in the third stream and the proportion of oligomers therein were measured and calculated, and the results are summarized in the table below.

[0082] In Comparative Examples 1 and 2, a separate heat transfer medium was not used, and the vaporization reaction section was heated to vaporize the material. [Table 3]

[0083] Referring to the table above, it can be clearly seen that, according to the embodiment of the present invention, lactic acid can be continuously vaporized to obtain a high-concentration lactic acid vapor, and at the same time, the content of lactic acid oligomers in the resultant product can be relatively reduced.

[0084] When using standard heating, the temperature of the lactic acid vapor generated is low, and the concentration of the lactic acid vapor is low, but the proportion of oligomers is relatively high.When using water vapor, the temperature of the lactic acid vapor generated is high, but the concentration of the lactic acid vapor is also low, but the proportion of oligomers is relatively high.

Claims

1. A step of mixing and atomizing a first stream in a liquid phase containing an aqueous lactic acid solution and a second stream in a gas phase containing lactic acid vapor; vaporizing the aqueous lactic acid solution by heat exchange between the first stream and the second stream; and obtaining a third stream of gas phase containing lactic acid monomers; Lactic acid vaporization method.

2. 2. The lactic acid vaporization method according to claim 1, wherein the aqueous lactic acid solution contained in the first stream has a lactic acid concentration of 20 to 99 wt %.

3. 2. The lactic acid vaporization method according to claim 1, wherein the aqueous lactic acid solution contained in the first stream has a lactic acid polymer concentration of 2 to 80 wt %.

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

5. 2. The lactic acid vaporization method according to claim 1, wherein the lactic acid vapor contained in the second stream has a lactic acid concentration of 20 to 80 wt %.

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

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

25.

8. 2. The method for vaporizing lactic acid according to claim 1, wherein at least a portion of the third stream is branched off and reused as the second stream.

9. A step of vaporizing lactic acid by the method according to any one of claims 1 to 8 to obtain lactic acid molecules; Dehydrating the lactic acid molecules to produce acrylic acid; and obtaining said acrylic acid, A method for producing acrylic acid.

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