Process for the preparation of acrylic acid

Abstract

The present disclosure relates to a method for preparing acrylic acid, and more particularly, to a method for preparing acrylic acid by dehydrating lactic acid molecules. According to the preparation method of the present disclosure, acrylic acid can be prepared from lactic acid with a high conversion rate and yield, and energy consumption can also be further reduced as compared with conventional methods.

Description

Technical Field

[0001] Cross-references in related fields

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0150320, filed with the Korean Intellectual Property Office on November 11, 2020, and Korean Patent Application No. 10-2021-0150793, filed with the Korean Intellectual Property Office on November 4, 2021, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This disclosure relates to methods for preparing acrylic acid, and more particularly, to methods for preparing acrylic acid by dehydrating lactic acid molecules. Background Technology

[0004] Acrylic acid is an organic compound with both carboxylic acid and unsaturated double bonds in its molecule. Its structure is very simple and it can be polymerized and transformed into various materials, thus making it suitable for a variety of industrial applications.

[0005] Specifically, acrylic acid is used as polyacrylic acid, granules, adhesives, coatings, etc. required for the production of superabsorbent polymers, or it can be used as a raw material for the preparation of other types of acrylate-based monomers, or it can be used as a raw material for polymerization with various other monomers such as acrylamide, acrylonitrile, styrene and α-olefins.

[0006] Such acrylic acid is typically used in the refining and separation of crude oil, such as in the production of propylene from naphtha cracking.

[0007] However, recently, with heightened focus on oil depletion and environmental issues, there is growing interest in methods for producing acrylic acid using eco-friendly raw materials. Summary of the Invention

[0008] Technical issues

[0009] One object of this disclosure is to provide a method for preparing acrylic acid from lactic acid with high conversion and yield.

[0010] Technical solution

[0011] This article provides a method for preparing acrylic acid, the method comprising the following steps: 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 contacting the vaporized lactic acid molecules with a dehydration catalyst; and a fourth step of obtaining acrylic acid, wherein the temperatures of the second to fourth steps are each independently regulated.

[0012] According to one embodiment of this disclosure, the second step can be performed at a temperature of about 200°C to about 290°C, preferably at about 200°C or higher, or about 230°C or higher, or about 250°C or higher, and at a temperature of about 290°C or lower, or about 270°C or lower, or about 260°C.

[0013] Furthermore, the second step can be performed in the presence of quartz.

[0014] According to another embodiment of this disclosure, the third step can be performed at a temperature above 350°C and about 400°C or lower, preferably at a temperature 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.

[0015] In addition, the dehydration catalyst may include at least one selected from calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts.

[0016] According to another embodiment of this disclosure, in the first step, based on the supply weight of lactic acid relative to the weight of the catalyst, the aqueous lactic acid solution can be supplied at a flow rate of about 0.01 / hour to about 10 / hour, or at a flow rate of about 0.1 / hour to about 5 / hour, or at a flow rate of about 0.1 / hour to about 1 / hour.

[0017] In this case, the concentration of the lactic acid aqueous solution in the first step can be from about 10% by weight to about 80% by weight.

[0018] According to another aspect of this disclosure, the first to fourth steps are carried out using a reactor equipped with a single reaction tube and a heating unit; the single reaction tube includes a supply unit supplying an aqueous lactic acid solution, a vaporization unit vaporizing the aqueous lactic acid solution, a catalyst unit contacting the vaporized lactic acid molecules with a dehydration catalyst, and an emission unit discharging acrylic acid; the heating unit includes, in a shape enclosing the single reaction tube, a first heating unit heating the vaporization unit, a second heating unit discontinuous with the first heating unit and extending to the boundary between the vaporization unit and the catalyst unit and to the front end of the catalyst unit, and a third heating unit discontinuous with the second heating unit and extending to the rear end of the catalyst unit, and the temperatures of the second to fourth steps are each independently regulated by the heating unit.

[0019] In this case, the first heating unit can be heated such that the interior of the vaporization unit of the single reaction tube is maintained at a temperature of about 200°C to about 290°C. This is the temperature condition for the second step described above, and specifically it can refer to 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.

[0020] Furthermore, the second and third heating units can be heated to maintain the interior of the catalyst unit in the individual reaction tube at a temperature above 350°C and about 400°C or lower. This refers to the temperature conditions for the aforementioned third step, and specifically, to a temperature condition 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.

[0021] In this case, the set temperature of the second heating unit can be higher than the set temperature of the third heating unit.

[0022] Specifically, the set temperature of the second heating unit can be about 15°C to about 30°C higher than the set temperature of the third heating unit.

[0023] As used herein, the terms “first,” “second,” etc., are used to describe various constituent elements, and these terms are used only to distinguish one constituent element from another.

[0024] The technical terms used herein are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0025] Unless the context explicitly indicates otherwise, the singular forms “a,” “a,” and “the” are intended to include the plural forms.

[0026] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of the said feature, integer, step, component, or combination thereof, but do not preclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0027] Furthermore, as used herein, when referring to a layer or element being formed “on” or “above” a layer or element, it means that the layer or element is formed directly on the layer or element, or that other layers or elements may be formed separately between layers, on an object, or on a substrate.

[0028] While this disclosure may take various forms and be modified in various ways, specific embodiments will be illustrated and described in detail below. However, it is not intended to limit this disclosure to the specific disclosure provided, and it should be understood that this disclosure includes all modifications, equivalents, or alternatives thereto without departing from the spirit and scope of this disclosure.

[0029] The contents of this disclosure will now be described in more detail.

[0030] According to one aspect of this disclosure, a method for preparing acrylic acid is provided, the method comprising the steps of: 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 contacting the vaporized lactic acid molecules with a dehydration catalyst; and a fourth step of obtaining acrylic acid, wherein the temperatures of the second to fourth steps are each independently regulated.

[0031] According to another aspect of this disclosure, the first to fourth steps are carried out using a reactor equipped with a single reaction tube and a heating unit; the single reaction tube includes a supply unit supplying an aqueous lactic acid solution, a vaporization unit vaporizing the aqueous lactic acid solution, a catalyst unit contacting the vaporized lactic acid molecules with a dehydration catalyst, and an emission unit discharging acrylic acid; the heating unit includes, in a shape enclosing the single reaction tube, a first heating unit heating the vaporization unit, a second heating unit discontinuous with the first heating unit and extending to the boundary between the vaporization unit and the catalyst unit and to the front end of the catalyst unit, and a third heating unit discontinuous with the second heating unit and extending to the rear end of the catalyst unit, and the temperatures of the second to fourth steps are each independently regulated by the heating unit.

[0032] The inventors have discovered that in a series of reactions to obtain acrylic acid by subjecting vaporized lactic acid molecules to a dehydration reaction in the presence of a catalyst, when the temperature of each step is independently adjusted by subdividing the vaporization and dehydration steps, the generation of byproducts can be reduced while the reaction efficiency can be improved, and the yield of acrylic acid and the conversion rate of lactic acid can be significantly increased, thus completing the present disclosure.

[0033] The dehydration reaction of vaporized lactic acid molecules in the presence of a catalyst can be represented by the following reaction mechanism.

[0034]

[0035] In other words, the dehydration reaction of lactic acid molecules can be described as follows: A catalyst releases the hydroxyl group attached to the α-position of the carbonyl group in the lactic acid molecule, and a catalyst also removes the hydrogen attached to the β-position of the carbonyl group to form an acrylate anion. Then, the hydrogen from the catalyst bonds with the carboxylate anion of the acrylate to form acrylic acid.

[0036] It is known that such a reaction proceeds well for vaporized lactic acid molecules in the presence of a catalyst, but it competes with reactions that form byproducts other than acrylic acid, such as i) aldehyde formation via decarboxylation or decarbonylation, ii) propionic acid formation via reduction of acrylic acid, iii) pentanedione formation via condensation, and iv) auto-esterification via dimerization, etc. Therefore, the reaction conditions need to be finely controlled.

[0037] First, the reactant in the first step, namely the lactic acid supplied as feed, is in the form of an aqueous lactic acid solution, which is preferably in the concentration range of about 10% by weight to about 80% by weight.

[0038] When the concentration of lactic acid is too low, the efficiency of the vaporization reaction in the vaporization step and the subsequent lactic acid dehydration reaction becomes too low. When the concentration of lactic acid is too high, the content of oligomers, such as dimers, in the lactic acid aqueous solution increases, which may reduce the efficiency of the lactic acid dehydration reaction of byproducts, potentially leading to problems that promote byproduct formation.

[0039] Furthermore, in the first step, based on the supply weight of lactic acid relative to the weight of the catalyst, the aqueous lactic acid solution can be supplied at a flow rate of about 0.01 / hour to about 10 / hour, or 0.1 / hour to about 5 / hour, or about 0.1 / hour to about 1 / hour.

[0040] When the supply of lactic acid aqueous solution is too small, the residence time of lactic acid at high temperatures increases, leading to a higher loss rate due to thermal decomposition. Furthermore, other side reactions may increase. When the supply of lactic acid aqueous solution is too large, lactic acid is not sufficiently vaporized by the heat source, and the temperature of the vaporization unit and the upper part of the catalyst bed decreases, potentially causing catalyst performance degradation.

[0041] Furthermore, lactic acid, as the feedstock, can be supplied via a carrier gas. An inert gas that does not affect the vaporization or dehydration reaction, such as nitrogen or a Group 18 gas, can be used as the carrier gas.

[0042] The flow rate of the carrier gas used for the reaction can be about 1 to about 1000 times, or about 10 to about 500 times, or about 20 to about 300 times the supply of the lactic acid aqueous solution.

[0043] According to one embodiment of this disclosure, the second step, namely, the vaporization reaction of lactic acid molecules, is carried out at a temperature 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 at a temperature of about 290°C or lower, or about 270°C or lower, or about 260°C.

[0044] When the temperature of the vaporization reaction is too low, the efficiency of the vaporization reaction decreases, which may lead to a decrease in the efficiency of the subsequent dehydration reaction. When the temperature of the vaporization reaction is too high, decarboxylation or decarbonylation occurs more significantly in the vaporized lactic acid molecules, which may promote the formation of aldehydes.

[0045] Furthermore, the second step can be carried out in the presence of quartz. Specifically, the quartz can be in the form of quartz wool with a large surface area or quartz particles.

[0046] That is, lactic acid molecules supplied to the supply unit can be adsorbed onto the surface of quartz wool or the like in the vaporization unit inside the reactor according to the flow of the carrier gas, and in this state, the lactic acid molecules can receive heat from the quartz wool or the like to be vaporized.

[0047] Furthermore, as described above, the reactor used for this reaction can be provided with a single reaction tube and a heating unit, and the heating unit can be shaped to enclose the single reaction tube. In this case, the first heating unit for heating the vaporization unit can be heated to maintain the interior of the vaporization portion of the single reaction tube at a temperature of about 200°C to about 290°C. This is the temperature condition for the second step described above, and specifically it can refer to 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.

[0048] However, throughout the specification, the temperatures of the reaction conditions for each reaction and the set temperatures of the first to third heating units located at various positions in the reactor can be different from each other. Specifically, the set temperatures of the first to third heating units can preferably be set to temperatures higher than their respective reaction conditions. This is likely because external gases and reactants are continuously supplied to the reactor according to the flow of the carrier gas; in particular, the temperature of the reactants supplied to the supply unit is generally lower than the temperature of the vaporization unit, and in the vaporization unit, the temperature continuously decreases due to the vaporization of lactic acid and water. Furthermore, the temperature of the vaporization unit, in which the vaporization reaction takes place, is lower than the temperature of the catalyst unit, in which the dehydration reaction takes place.

[0049] From this perspective, the first heating unit can preferably be set to the target temperature of the vaporization unit, that is, about 15°C to about 30°C higher than the preferred temperature of the vaporization reaction described above.

[0050] Then, the gaseous reaction product containing vaporized lactic acid monomers continues to move with the flow of the carrier gas to the catalyst unit in which the catalyst is present, and can undergo a dehydration reaction, i.e., the third step.

[0051] According to another embodiment of this disclosure, the third step is carried out at a temperature above 350°C and about 400°C or lower, preferably at a temperature 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.

[0052] When the temperature in step 3 is too low, there may be a significant reduction in lactic acid conversion and acrylic acid yield. When the temperature in step 3 is too high, it further promotes i) aldehyde formation through decarboxylation or decarbonylation, ii) propionic acid formation through reduction of acrylic acid, iii) pentanedione formation, etc., which may lead to an increase in byproducts.

[0053] Furthermore, as mentioned above, the temperature of the catalyst unit, which serves as the dehydration reaction condition, and the set temperatures of the second and third heating units located at various positions in the reactor can be different from each other.

[0054] Specifically, the second heating unit may be located inside the reactor, encompassing i) the boundary portion between the vaporization unit and the catalyst unit and ii) the portion corresponding to the front end of the catalyst unit in a single reaction tube. The third heating unit may be shaped to encompass iii) the portion corresponding to the rear end of the catalyst unit in a single reaction tube.

[0055] Furthermore, the second and third heating units can be heated such that the interior of the catalyst unit in the individual reaction tube is maintained at a temperature above 350°C and about 400°C or lower. This is the temperature condition for the aforementioned third step, and can refer to a temperature condition 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.

[0056] In this case, it is preferable that the set temperature of the second heating unit is higher than that of the third heating unit. Specifically, it is preferable that the set temperature of the second heating unit is about 15°C to about 30°C higher than that of the third heating unit.

[0057] For example, the second and third heating units are preferably set to a temperature higher than the target temperature of the catalyst unit, that is, about 15°C to about 30°C higher than the preferred temperature for the dehydration reaction described above. In particular, the second heating unit can be set to a higher temperature than the third heating unit, and for example, the second heating unit can be set to a temperature about 15°C to about 30°C higher.

[0058] As described above, due to the type of reaction in which external gases and reactants are continuously supplied to the reactor according to the flow of the carrier gas, the temperature at the front end of the vaporization unit and the catalyst unit inevitably continues to decrease. This is because the temperature at the front end of the vaporization unit and the catalyst unit may decrease, thereby significantly reducing the overall reaction efficiency.

[0059] Under normal circumstances, to prevent these problems, methods such as setting the overall temperature of the reactor to a high level before the reaction proceeds or preheating the reactor to the target temperature are used before the reaction takes place. However, in such cases, energy is wasted unnecessarily, and the efficiency of the reaction may be reduced due to the aforementioned side reactions under high-temperature conditions, while the problem of temperature reduction at the front end of the catalyst unit remains difficult to solve.

[0060] In the context of this disclosure, the temperatures of the vaporization unit, the boundary between the vaporization unit and the catalyst unit, the front end of the catalyst unit, and the rear end of the catalyst unit are set differently according to the needs of each reaction. In particular, a separate heating unit capable of supplying heat, i.e., a second heating unit, is positioned at the boundary between the vaporization unit and the catalyst unit where the temperature conditions change rapidly, thereby further improving energy efficiency and reaction efficiency.

[0061] Furthermore, the dehydration catalyst may include at least one selected from calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts, and other reaction conditions may be used without any particular limitation, provided that they are those commonly used in the art to which this disclosure pertains and do not contradict the scope defined herein.

[0062] More specifically, dehydration catalysts may include CaSO4 / Na2SO4; Na4P2O7 / CaSO4; Na4P2O7 / Ca3(PO4)2; NaH2PO4-NaHCO3 / SiO2; AlPO4-NH3; Ca3(PO4)2 / CaSO4; Ca2P2O7; Ca5(PO4)3(OH), etc.

[0063] Beneficial effects

[0064] According to the preparation method disclosed herein, acrylic acid can be prepared from lactic acid with high conversion and yield, and energy consumption can be further reduced compared to conventional methods. Detailed Implementation

[0065] The effects and functions of the invention will be described in more detail below with reference to specific embodiments thereof. However, these embodiments are presented for illustrative purposes only, and the scope of the invention is not limited thereto in any way.

[0066] <Example>

[0067] A reaction tube made of quartz with an inner diameter of 7 / 8 inches and a length of 860 mm was prepared as a single reaction tube.

[0068] Adding non-reactive glass tubes and quartz wool prevents the quartz sand from spilling in an area of ​​approximately 150 mm to approximately 300 mm from the top of a single reaction tube, and fills the area with quartz sand to form a vaporization unit.

[0069] As a catalyst, a catalyst obtained by molding calcium phosphate catalyst into cylindrical pellets with a diameter of about 3 mm and a length of about 3 mm was used.

[0070] Then, a non-reactive glass tube and quartz wool are placed in an area about 300 mm from the lower end of the vaporization section to prevent the catalyst from tipping over, and about 50 g of catalyst is filled in it to form a catalyst unit.

[0071] A first heating unit with a length of approximately 200 mm is arranged approximately 100 mm downwards from the top of the single reaction tube, in a shape that surrounds the entire area of ​​the vaporization unit corresponding to the single reaction tube.

[0072] Alternatively, a second heating unit with a length of approximately 100 mm may be arranged from the rear end of the first heating unit, in the shape of the boundary portion between the vaporization unit and the catalyst unit surrounding the single reaction tube and the region corresponding to the front end of the catalyst unit.

[0073] Alternatively, a third heating unit with a length of approximately 200 mm may be arranged from the rear end of the second heating unit in a shape that surrounds the region corresponding to the rear end of the catalyst unit of a single reaction tube.

[0074] Alternatively, a fourth heating unit with a length of approximately 200 mm may be arranged from the rear end of the second heating unit in a shape that surrounds the region corresponding to the discharge unit of a single reaction tube.

[0075] Thermocouples are placed at the front and rear ends of the catalyst unit in a single reaction tube to measure the internal temperature.

[0076] Nitrogen gas was used as the carrier gas at a flow rate of approximately 80 ml / min. A lactic acid aqueous solution with a concentration of approximately 40% by weight was supplied to the reactor at a flow rate of approximately 0.4 ml / min. The density of the supplied lactic acid aqueous solution was approximately 1.08 g / ml. Based on the amount of lactic acid, the supply rate of the lactic acid aqueous solution was approximately 10.37 g / h, which was calculated to be approximately 0.21 g / h for a reference weight (1 g) of catalyst (50 g).

[0077] Product samples obtained from the emission unit were collected, cooled to approximately 4°C in a condenser, and collected in liquid phase. The amount of acrylic acid obtained was determined by HPLC.

[0078] During the reaction, the set temperatures of the first to fourth heating units are made different from each other, and the temperatures at the front and rear ends of the catalyst unit are measured while the vaporization and dehydration reactions are taking place.

[0079] The measurement results are summarized in the table below.

[0080] [Table 1]

[0081]

[0082] Referring to Table 1, it can be clearly determined that a method for preparing acrylic acid according to one embodiment of this disclosure can prepare acrylic acid from lactic acid with high conversion and high yield.

[0083] Furthermore, it can be determined that, as in Comparative Examples 1 and 2, when the temperature of the first heating unit (lactic acid vaporization, second stage) is increased to 300°C or higher, even if the temperature at the front end of the catalyst unit is set similarly to that in Examples 1 and 2, the rate of acetaldehyde formation is higher than in Examples 1 and 2. This appears to be due to the fact that the excessively high temperature of lactic acid vaporization makes the decarboxylation or decarbonylation reaction more dominant than the dehydration reaction.

[0084] Comparing the results of the embodiments and comparative examples, it can be determined that when the temperatures of each step of the lactic acid vaporization reaction in one embodiment of the present disclosure are independently adjusted, such as the step of supplying an aqueous lactic acid solution to the reactor using a carrier gas, the step of vaporizing the aqueous lactic acid solution, the step of contacting the vaporized lactic acid molecules with a dehydration catalyst, and the step of obtaining acrylic acid, side reactions such as the generation of acetaldehyde can be effectively suppressed, while maximizing the lactic acid conversion rate and the acrylic acid yield.

Claims

1. A method for preparing acrylic acid, comprising the following steps: The first step involves supplying an aqueous lactic acid solution to the reactor using a carrier gas. The second step of vaporizing the lactic acid aqueous solution; The third step is to bring the vaporized lactic acid molecules into contact with the dehydration catalyst; as well as The fourth step in obtaining acrylic acid, in: The first to the fourth steps are carried out using a reactor equipped with a single reaction tube and a heating unit; The single reaction tube includes a supply unit in which an aqueous lactic acid solution is supplied, a vaporization unit for vaporizing the aqueous lactic acid solution, a catalyst unit for contacting the vaporized lactic acid molecules with a dehydration catalyst, and an emission unit for discharging acrylic acid. The heating unit, shaped to enclose the single reaction tube, includes a first heating unit that heats the vaporization unit, a second heating unit discontinuous with the first heating unit that heats the boundary between the vaporization unit and the catalyst unit and the front end of the catalyst unit, and a third heating unit discontinuous with the second heating unit that heats the rear end of the catalyst unit. The temperatures of each of the second to fourth steps are independently adjusted by the heating unit; and The set temperature of the second heating unit is higher than the set temperature of the third heating unit. The dehydration catalyst includes at least one selected from calcium phosphate-based catalysts, sodium phosphate-based catalysts, and aluminum phosphate-based catalysts.

2. The method for preparing acrylic acid according to claim 1, wherein: The second step is carried out at a temperature of 200°C to 290°C.

3. The method for preparing acrylic acid according to claim 1, wherein: The second step is carried out in the presence of quartz.

4. The method for preparing acrylic acid according to claim 1, wherein: The third step is carried out at a temperature above 350°C and 400°C or lower.

5. The method for preparing 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 per hour, based on the supply weight of lactic acid relative to the weight of the catalyst.

6. The method for preparing acrylic acid according to claim 1, wherein: The concentration of the lactic acid aqueous solution in the first step is from 10% to 80% by weight.

7. The method for preparing acrylic acid according to claim 1, wherein: The first heating unit is heated such that the interior of the vaporization unit of the single reaction tube is maintained at a temperature of 200°C to 290°C.

8. The method for preparing acrylic acid according to claim 1, wherein: The second heating unit and the third heating unit are heated such that the interior of the catalyst unit in the single reaction tube is maintained at a temperature above 350°C and 400°C or lower.

9. The method for preparing acrylic acid according to claim 1, wherein: The set temperature of the second heating unit is 15°C to 30°C higher than the set temperature of the third heating unit.

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