Method for producing acrylic acid

Abstract

The present invention relates to a method for producing acrylic acid, and more particularly to a method for producing acrylic acid by dehydrating lactic acid molecules.The method of the present invention can produce acrylic acid from lactic acid with a high conversion rate and yield, while further reducing energy consumption compared to conventional methods.

Description

Technical Field

[0001] Cross-reference to related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0150320 filed on November 11, 2020, and Korean Patent Application No. 10-2021-0150793 filed on November 4, 2021, 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 for producing acrylic acid, and more particularly, to a method for producing acrylic acid by dehydrating lactic acid molecules.

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 can be converted into various substances. Since it is polymerizable, it is used in various industrial fields.

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

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

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

Summary of the Invention

Problems to be Solved by the Invention

[0007] This specification aims to provide a method for producing acrylic acid from lactic acid with high conversion and yield.

Means for Solving the Problems

[0008] This specification provides a method for producing acrylic acid, which includes a first step of supplying an aqueous lactic acid solution to a reactor using a carrier gas, a second step of vaporizing the aqueous lactic acid solution, a third step of bringing the vaporized lactic acid molecules into contact with a dehydration catalyst, and a fourth step of obtaining acrylic acid, wherein the temperatures of the second to fourth steps are independently adjusted.

[0009] According to one embodiment of the invention, the second step is carried out under temperature conditions of about 200°C to about 290°C, preferably at a temperature of about 200°C or higher, or about 230°C or higher, or about 250°C or higher, and about 290°C or lower, or about 270°C or lower, or about 260°C.

[0010] And the second step is carried out in the presence of quartz.

[0011] According to another embodiment of the invention, the third step is carried out under temperature conditions above 350°C and about 400°C or lower, preferably above 350°C, or about 355°C or higher, or about 360°C or higher, and about 400°C or lower, or about 390°C or lower, or about 380°C or lower.

[0012] And the dehydration catalyst can include one or more selected from the group consisting of calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts.

[0013] According to another embodiment of the invention, in the first step, when based on the supply weight of lactic acid relative to the weight of the catalyst, the aqueous lactic acid solution is supplied at a flow rate of about 0.01 to about 10 / hour, or 0.1 to about 5 / hour, or about 0.1 to about 1 / hour.

[0014] And at this time, the concentration of the aqueous lactic acid solution in the first step is preferably about 10 to about 80 wt%.

[0015] According to another aspect of the invention, the first to fourth steps are performed using a reactor in the form of a single reaction tube and a heating unit; the single reaction tube includes a supply unit to which an aqueous lactic acid solution is supplied, a vaporization unit that vaporizes the aqueous lactic acid solution, a catalyst unit that brings the vaporized lactic acid molecules into contact with a dehydration catalyst, and a discharge unit that discharges acrylic acid; the heating unit surrounds the single reaction tube and includes a first heating unit for heating the vaporization unit, a second heating unit that is discontinuous with the first heating unit and heats a boundary site between the vaporization unit and the catalyst unit and a front stage of the catalyst unit, and a third heating unit that is discontinuous with the second heating unit and heats a subsequent stage of the catalyst unit; the temperatures in the second to fourth steps may be independently adjusted by the heating unit.

[0016] At this time, the first heating unit may be configured to heat such that the inside of the vaporization unit of the single reaction tube is maintained at a temperature condition of about 200°C to about 290°C. This refers to the temperature condition in the second step described above, specifically, a temperature condition of about 200°C to about 290°C, preferably about 200°C or higher, or about 230°C or higher, or about 250°C or higher, and about 290°C or lower, or about 270°C or lower, or about 260°C.

[0017] And the second heating unit and the third heating unit may be configured to heat such that the inside of the catalyst unit of the single reaction tube is maintained at a temperature condition above 350°C and below about 400°C. This refers to the temperature condition in the third step described above, a temperature condition above 350°C and below about 400°C, preferably above 350°C, or about 355°C or higher, or about 360°C or higher, and below about 400°C, or about 390°C or lower, or about 380°C or lower.

[0018] At this time, the set temperature of the second heating unit is higher than the set temperature of the third heating unit.

[0019] Specifically, it is preferable that the set temperature of the second heating unit is about 15°C to about 30°C higher than the set temperature of the third heating unit.

[0020] In the present invention, terms such as first and second are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another component.

[0021] Also, the terms used in this specification are used only for the purpose of explaining exemplary embodiments and are not intended to limit the present invention.

[0022] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, terms such as "including", "comprising", or "having" are for the purpose of explaining 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.

[0024] Also, in this specification, when each layer or element is referred to as being "formed on" each layer or element, it means that each layer or element is directly formed on each layer or element, or that other layers or elements may be additionally formed between the layers, on the object, or on the substrate.

[0025] The present invention can have various forms with various modifications added, but specific embodiments are illustrated and described in detail below. However, this does not limit the present invention to a specific disclosed form, and it should be understood that it includes all modifications, equivalents, and alternatives included in the spirit and technical scope of the present invention.

[0026] Hereinafter, the present invention will be described in detail. According to one aspect of the present invention, there is provided a method for producing acrylic acid, including: a first step of supplying an aqueous lactic acid solution to a reactor using a carrier gas; a second step of vaporizing the aqueous lactic acid solution; a third step of bringing the vaporized lactic acid molecules into contact with a dehydration catalyst; and a fourth step of obtaining acrylic acid, wherein the temperatures of the second to fourth steps are independently adjusted.

[0027] According to another aspect of the invention, the first to fourth steps are performed using a reactor in a form including a single reaction tube and a heating unit; the single reaction tube includes a supply unit to which an aqueous lactic acid solution is supplied, a vaporization unit that vaporizes the aqueous lactic acid solution, a catalyst unit that brings the vaporized lactic acid molecules into contact with a dehydration catalyst, and a discharge unit that discharges acrylic acid; the heating unit surrounds the single reaction tube, and includes a first heating unit for heating the vaporization unit, a second heating unit that is discontinuous with the first heating unit and heats a boundary site between the vaporization unit and the catalyst unit and a front stage of the catalyst unit, and a third heating unit that is discontinuous with the second heating unit and heats a subsequent stage of the catalyst unit; the temperatures in the second to fourth steps may be independently adjusted by the heating unit.

[0028] The inventors of the present invention have found that in a series of reactions for obtaining acrylic acid by allowing a dehydration reaction to proceed in the presence of a catalyst in vaporized lactic acid molecules, when the vaporization stage and the dehydration stage are subdivided and the temperature of each stage is independently adjusted, while reducing the generation of by-products, the reaction efficiency can be increased, and the yield of acrylic acid and the lactic acid conversion rate can be remarkably improved, and thus the present invention has been completed.

[0029] The dehydration reaction performed in the presence of a catalyst in vaporized lactic acid molecules is represented by the following reaction mechanism.

Chemical formula

[0030] That is, in the dehydration reaction of lactic acid molecules, the hydroxy group linked to the carbonyl alpha position of the lactic acid molecules is detached by the catalyst, and while the hydrogen linked to the carbonyl beta position is also removed by the catalyst, an acrylic acid anion is formed, and then acrylic acid is generated while the hydrogen of the catalyst is linked to the carboxylic acid anion of acrylic acid.

[0031] Such reactions are known to proceed well in the presence of a catalyst with respect to vaporized lactic acid molecules. However, since they compete with reactions that form other by-products that are not acrylic acid, such as i) an aldehyde formation reaction by decarboxylation or decarbonylation of the carboxyl group, ii) a propanoic acid formation reaction by reduction of acrylic acid, iii) a pentanedione formation reaction by condensation, and iv) an auto-esterification by dimerization to form a cyclic ester, it is necessary to finely adjust the reaction conditions.

[0032] First, in the first stage, the reactant, that is, lactic acid supplied to the feed, is preferably in the form of an aqueous lactic acid solution and in a concentration range of about 10 to about 80 wt%.

[0033] When the concentration of lactic acid is excessively low, there is a problem that the efficiency of the vaporization reaction in the vaporization stage and the efficiency of the subsequent lactic acid dehydration reaction become excessively low. When the concentration of lactic acid is excessively high, the content of oligomers such as dimers in the aqueous lactic acid solution increases, the efficiency of the by-product lactic acid dehydration reaction decreases, and problems such as the promotion of by-product formation may occur.

[0034] And in the first stage, when based on the weight of the supplied lactic acid with respect to the weight of the catalyst, the aqueous lactic acid solution is supplied at a flow rate of about 0.01 and about 10 / hour, or 0.1 to about 5 / hour, or about 0.1 to about 1 / hour.

[0035] When the supply amount of the aqueous lactic acid solution is excessively small, as the residence time of lactic acid at a high temperature becomes longer, the loss ratio due to thermal decomposition increases, and other side reactions may also increase. When the supply amount of the aqueous lactic acid solution is excessively large, lactic acid cannot be sufficiently vaporized by the heat source, and problems such as a decrease in the temperature at the upper end of the vaporization section and the catalyst layer and a decrease in catalyst performance may occur.

[0036] Then, the lactic acid supplied to the feed is supplied by a carrier gas. As the carrier gas used at this time, an inert gas that does not affect the vaporization reaction or dehydration reaction, such as nitrogen or a Group 18 gas, can be used.

[0037] The flow rate of the carrier gas used in the reaction can be an amount about 1 to about 1000 times, or about 10 to about 500 times, or about 20 to about 300 times that of the supplied aqueous lactic acid solution.

[0038] According to one embodiment of the invention, the second step, i.e., the vaporization reaction of lactic acid molecules, is carried out under temperature conditions of about 200°C to about 290°C, preferably about 200°C or higher, or about 230°C or higher, or about 250°C or higher, and about 290°C or lower, or about 270°C or lower, or about 260°C.

[0039] When the temperature of the vaporization reaction is excessively low, the efficiency of the vaporization reaction decreases, and as a result, the efficiency of the subsequent dehydration reaction also decreases. When the temperature of the vaporization reaction is excessively high, decarboxylation or decarbonylation of the vaporized lactic acid molecules may occur more predominantly, resulting in the problem of promoting the production of aldehydes.

[0040] Then, the second step is carried out in the presence of quartz. Specifically, the quartz may be in the form of quartz wool with a large surface area or quartz particles.

[0041] That is, the lactic acid molecules supplied to the supply unit are adsorbed on the surface of quartz wool or the like in the vaporization section inside the reactor by the flow of the carrier gas, and in this state, heat is supplied from quartz wool or the like and vaporization can occur.

[0042] And, as described above, the reactor used for such a reaction may include a single reaction tube and a heating unit, and the heating unit may be in a form surrounding the single reaction tube. At this time, the first heating unit for heating the vaporization unit may be configured to heat the inside of the vaporization unit of the single reaction tube to be maintained at a temperature condition of about 200°C to about 290°C. This refers to the temperature condition of the second stage described above, specifically, the temperature condition of about 200°C to about 290°C, preferably about 200°C or higher, or about 230°C or higher, or about 250°C or higher, and about 290°C or lower, or about 270°C or lower, or about 260°C.

[0043] However, throughout this specification, the temperature as the reaction condition of each reaction and the set temperatures of the first to third heating units located at each part of the reactor may be different from each other. Specifically, the set temperatures of the first to third heating units are preferably set higher than the temperatures of the corresponding reaction conditions. This is because the external gas and the reactants are continuously supplied into the reactor by the flow of the carrier gas. In particular, it is common that the temperature of the reactants supplied to the supply unit is lower than the temperature of the vaporization unit. Also, in the vaporization unit, the temperature continuously decreases due to the vaporization of lactic acid and water. Furthermore, this is due to the fact that the temperature of the vaporization unit where the vaporization reaction progresses is lower than the temperature of the catalyst unit where the dehydration reaction progresses.

[0044] From this perspective, the first heating unit is preferably set about 15 to about 30°C higher than the target temperature of the vaporization unit, that is, the preferable temperature of the vaporization reaction described above.

[0045] And the gaseous reactants containing vaporized lactic acid monomers continuously move to the catalyst unit where the catalyst exists by the flow of the carrier gas and are input into the dehydration reaction, that is, the third stage.

[0046] According to another embodiment of the invention, the third stage is carried out under temperature conditions of exceeding 350°C and about 400°C or lower, preferably exceeding 350°C, or about 355°C or higher, or about 360°C or higher, and about 400°C or lower, or about 390°C or lower, or about 380°C or lower.

[0047] When the temperature in the third stage is excessively low, there is a problem that the lactic acid conversion rate and the yield of acrylic acid significantly decrease. When the temperature in the third stage is excessively high, i) an aldehyde generation reaction by decarboxylation or decarbonylation, ii) a propanoic acid generation reaction by reduction of acrylic acid, iii) a pentanedione generation reaction by condensation, etc. may be further promoted, and there may be a problem of an increase in by-products.

[0048] And, as described above, the temperature of the catalyst part as the dehydration reaction condition and the set temperatures of the second and third heating parts located at each part of the reactor may be different from each other.

[0049] Specifically, the second heating part may be in a form that surrounds the corresponding part in a single reaction tube in order to heat i) the boundary part between the vaporization part and the catalyst part and ii) the front stage of the catalyst part inside the reactor. The third heating part may be in a form that surrounds the corresponding part in a single reaction tube in order to heat iii) the rear stage of the catalyst part.

[0050] And, the second heating part and the third heating part may be those that heat so that the inside of the catalyst part of the single reaction tube is maintained under temperature conditions exceeding 350°C and about 400°C or less. This may refer to the temperature conditions in the third stage described above, which are exceeding 350°C and about 400°C or less, preferably exceeding 350°C, or about 355°C or higher, or about 360°C or higher, and about 400°C or less, or about 390°C or less, or about 380°C or less.

[0051] At this time, it is preferable that the set temperature of the second heating part is higher than the set temperature of the third heating part. Specifically, it is preferable that the set temperature of the second heating part is about 15°C to about 30°C higher than the set temperature of the third heating part.

[0052] For example, the second and third heating units are preferably set to be about 15 to about 30 °C higher than the target temperature of the catalyst unit, that is, the preferred temperature of the dehydration reaction described above. In particular, the second heating unit can be set to a higher temperature than the third heating unit, for example, about 15 °C to about 30 °C higher.

[0053] As described above, depending on the form of the reaction in which the external gas and the reactants are continuously supplied into the reactor by the flow of the carrier gas, the temperatures of the vaporization unit and the front stage of the catalyst unit continuously decrease. However, when the temperature of the entire reactor is set to be the same without distinguishing each part, the temperatures of the vaporization unit and the front stage of the catalyst unit become low, and the efficiency of the entire reaction may be greatly reduced.

[0054] In the case of the prior art, in order to prevent this, methods such as setting the overall temperature of the reactor higher or preheating the reactor before the reaction proceeds and then introducing it into the reaction after reaching the target temperature were used. However, in this case, energy is wasted unnecessarily, and the efficiency of the reaction may decrease due to the side reactions described above under high temperature conditions, while it is still difficult to solve the problem that the temperature of the front stage of the catalyst unit becomes low.

[0055] In the case of the present invention, the temperatures of the vaporization unit, the boundary between the vaporization unit and the catalyst unit, the front stage of the catalyst unit, and the rear stage of the catalyst unit are set differently according to the requirements of each reaction. In particular, a separate heating unit, that is, the second heating unit, which can supply heat to the boundary between the vaporization unit and the catalyst unit where the change in temperature conditions becomes abrupt, is provided. Thus, while further improving the energy efficiency, the reaction efficiency can also be improved.

[0056] The dehydration catalyst can include one or more 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 special limitations as long as they are generally used in the technical field to which the present invention belongs and do not conflict with the content defined in this specification.

[0057] 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), etc.

Advantages of the Invention

[0058] According to the production method of the present invention, acrylic acid can be produced from lactic acid with high conversion and yield, while further saving energy consumption compared to the existing methods.

Embodiments for Carrying Out the Invention

[0059] Hereinafter, the actions and effects of the invention will be described in more detail through specific examples of the invention. However, such examples are merely presented as examples of the invention and do not define the scope of the invention.

Examples

[0060] As a single reaction tube, a quartz reaction tube (reaction cylinder) with an inner diameter of 7 / 8 inch and a length of 860 mm was prepared.

[0061] From the upper end to the lower side of the single reaction tube, a non-reactive glass tube and quartz wool were placed at a position from about 150 mm to about 300 mm so that quartz sand would not spill, and quartz sand was filled to form a vaporization section.

[0062] As the catalyst, calcium phosphate catalyst formed into cylindrical pellets with a diameter of about 3 mm and a length of about 3 mm was used.

[0063] Then, in a region with a length of about 300 mm from the lower end of the vaporization section, a non-reactive glass tube and quartz wool were placed so that the catalyst would not spill, and about 50 g of the catalyst was filled therein to form a catalyst section.

[0064] A first heating section with a length of about 200 mm was provided in a form surrounding the entire region corresponding to the vaporization section of the single reaction tube, starting from a position about 100 mm downward from the upper end of the single reaction tube.

[0065] Separately from this, a second heating section with a length of about 100 mm was provided in a form surrounding the region corresponding to the boundary site between the vaporization section and the catalyst section of the single reaction tube and the front stage of the catalyst section, starting from the subsequent stage of the first heating section.

[0066] Separately from this, a third heating section with a length of about 200 mm was provided in a form surrounding the region corresponding to the subsequent stage of the catalyst section of the single reaction tube, starting from the subsequent stage of the second heating section.

[0067] Separately from this, Third heating unit a fourth heating section with a length of about 200 mm was provided in a form surrounding the region corresponding to the discharge section of the single reaction tube, starting from the subsequent stage of

[0068] Thermocouples were provided at the front stage and the subsequent stage of the catalyst section of the single reaction tube so that the internal temperature could be measured.

[0069] Nitrogen was used as the carrier gas, the flow rate was set to about 80 ml / min, and an aqueous lactic acid solution with a concentration of about 40 wt% was set to a flow rate of about 0.4 ml / min and supplied to the reactor. The density of the supplied aqueous lactic acid solution was about 1.08 g / ml, and the supply rate of the aqueous lactic acid solution was about 10.37 g / hour based on the amount of lactic acid, and was calculated to be about 0.21 / hour with respect to the reference weight (1 g) of the supplied catalyst (50 g).

[0070] Product samples obtained from the discharge section were collected, cooled to about 4 °C with a condenser and collected in the liquid phase, and the amount of acrylic acid obtained using HPLC was confirmed.

[0071] During the reaction, the set temperatures of the first to fourth heating sections were made different, and the temperatures at the front stage and the subsequent stage of the catalyst section were measured while allowing the vaporization reaction and the dehydration reaction to proceed.

[0072] The measurement results were summarized in the following table.

Table 1

[0073] Referring to Table 1, it can be clearly confirmed that the method for producing acrylic acid according to an embodiment of the present invention can produce acrylic acid from lactic acid with high conversion and yield.

[0074] Also, when the temperature of the first heating section (lactic acid vaporization, second stage) rises to 300°C or higher as in Comparative Examples 1 and 2, although the temperature of the front stage of the catalyst section was set similarly to Examples 1 and 2, it can be confirmed that the ratio of acetaldehyde generation is even higher than that in Examples 1 and 2. This is considered to be due to the fact that the temperature of lactic acid vaporization is excessively high, and the decarboxylation reaction or decarbonylation reaction is more dominant than the dehydration reaction.

[0075] Comparing the results of the above examples and comparative examples, when the temperature of each stage of the lactic acid vaporization reaction, such as the stage of supplying an aqueous lactic acid solution to the reactor using a carrier gas, the stage of vaporizing the aqueous lactic acid solution, the stage of bringing the vaporized lactic acid molecules into contact with a dehydration catalyst, and the stage of obtaining acrylic acid, is independently adjusted as in an embodiment of the present invention, it can be seen that while the lactic acid conversion rate and the yield of acrylic acid can be maximized, side reactions such as acetaldehyde generation can be efficiently suppressed.

Claims

1. A first step of feeding an aqueous solution of lactic acid into a reactor using a carrier gas; A second step of vaporizing the aqueous lactic acid solution; A third step of contacting the vaporized lactic acid molecules with a dehydration catalyst to produce acrylic acid; and a fourth stage for discharging the produced acrylic acid; The temperatures of the second to fourth stages are independently adjusted. A method for producing acrylic acid, comprising the steps of: The second step is carried out at a temperature of 230° C. to 250° C. The third step is carried out at a temperature of 355° C. or more and 390° C. or less. method.

2. 2. The process for producing acrylic acid according to claim 1, wherein the second stage is carried out in the presence of quartz.

3. 3. The method for producing acrylic acid according to claim 1 or 2, wherein the third step is carried out at a temperature of 360° C. or more and 380° C. or less.

4. 4. The method for producing acrylic acid according to claim 1, wherein the dehydration catalyst comprises at least one selected from the group consisting of calcium phosphate catalysts, sodium phosphate catalysts, and aluminum phosphate catalysts.

5. 5. The method for producing acrylic acid according to claim 1, wherein in the first step, the aqueous lactic acid solution is supplied at a flow rate of 0.01 to 10 / hour based on the weight of lactic acid supplied relative to the weight of the catalyst.

6. The method for producing acrylic acid according to any one of claims 1 to 5, wherein the concentration of the aqueous lactic acid solution in the first stage is 10 to 80 wt%.

7. The first to fourth steps are carried out using a reactor having a single reaction tube and a heating section; The single reaction tube includes a supply section to which an aqueous lactic acid solution is supplied, a vaporization section to vaporize the aqueous lactic acid solution, a catalyst section to contact the vaporized lactic acid molecules with a dehydration catalyst, and a discharge section to discharge acrylic acid; the heating unit includes a first heating unit surrounding the single reaction tube and configured to heat the vaporizer unit, a second heating unit that is discontinuous with the first heating unit and configured to heat a boundary between the vaporizer unit and a catalyst unit and a front portion of the catalyst unit, and a third heating unit that is discontinuous with the second heating unit and configured to heat a rear portion of the catalyst unit, The temperatures of the second to fourth stages are independently adjusted by the heating unit. the first heating unit is heated so that the inside of the vaporizing unit of the single reaction tube is maintained at a temperature condition of 230° C. to 250° C.; the second heating section and the third heating section heat the inside of the catalyst section of the single reaction tube so as to maintain the temperature condition of 355° C. or more and 390° C. or less; The method for producing acrylic acid according to claim 1 .

8. the second heating section and the third heating section heat the inside of the catalyst section of the single reaction tube so as to maintain the temperature condition of 360° C. or more and 380° C. or less; The method for producing acrylic acid according to claim 7.

9. The method for producing acrylic acid according to claim 7 or 8, wherein the set temperature of the second heating section is higher than the set temperature of the third heating section.

10. The method for producing acrylic acid according to claim 9, wherein the set temperature of the second heating section is 15° C. to 30° C. higher than the set temperature of the third heating section.

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