Method for preparation of acrylic acid

Abstract

The present invention provides a method for preparation of acrylic acid, comprising a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series, wherein a first stage crystallization unit from among the two or more crystallization units includes a crystallizer having a crystallization temperature of -20°C to -10°C.

Description

Method for producing acrylic acid

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0126965, filed September 22, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for producing acrylic acid, and more particularly, to a method for producing high-purity acrylic acid using a continuous crystallization process.

[0005] Acrylic acid is generally produced by a gas phase oxidation reaction of compounds such as propane, propylene, and acrolein in the presence of a catalyst. For example, in a reactor, propane, propylene, etc. are converted to acrylic acid via acrolein through a gas phase oxidation reaction in the presence of an appropriate catalyst, and a mixed gas containing acrylic acid, unreacted propane or propylene, acrolein, inert gases, carbon dioxide, water vapor, and various organic by-products (acetic acid, low-boiling-point by-products, high-boiling-point by-products, etc.) from the above reaction is obtained at the rear end of the reactor.

[0006] The above acrylic acid-containing mixed gas is recovered as an acrylic acid solution by contacting it with an absorption solvent such as water in an absorption tower. In addition, subsequent processes such as extraction, distillation, and purification are typically performed to obtain the acrylic acid contained in the acrylic acid solution.

[0007] However, because the specific heat of the absorption solvent, such as water, used in the absorption tower is high, a considerably high amount of energy is required to separate byproducts from the acrylic acid solution containing the absorption solvent through processes such as distillation. In addition, processes such as high-temperature distillation can produce polymers of acrylic acid, a reactive monomer, and there is the problem of the need for periodic cleaning.

[0008] Meanwhile, a crystallization process is sometimes performed to obtain acrylic acid contained in the acrylic acid solution, but since acetic acid, which is an organic byproduct, has a similar melting point to the acrylic acid, if a large amount of acetic acid is introduced into the crystallization process, it is not possible to obtain acrylic acid of the desired purity with only one crystallization process, and it is difficult to obtain acrylic acid at the desired level.

[0009] Therefore, there is an urgent need to introduce a technology that can increase the final yield of acrylic acid while obtaining high-purity acrylic acid from an acrylic acid solution.

[0010] The problem to be solved in the present invention is to provide a method for producing acrylic acid, which can increase the final yield of acrylic acid contained in the acrylic acid solution and ultimately obtain high-purity acrylic acid, in order to solve the problem mentioned in the background technology of the above invention.

[0011] According to one embodiment of the present invention for solving the above problem, the present invention is performed by including a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series, and acrylic acid contained in an acrylic acid solution introduced into the crystallizer of each stage is crystallized in the crystallizer of each stage to obtain a suspension including acrylic acid crystals, and the suspension is supplied to the solid-liquid separator of each stage, and the suspension is solid-liquid separated in the solid-liquid separator of each stage to obtain a concentrated acrylic acid solution and a mother liquor, wherein the mother liquor is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream is circulated to a crystallizer or mother liquor treatment process of a stage upstream of the solid-liquid separator to which the mother liquor is separated, and the second mother liquor stream is circulated to a crystallizer of a stage to which the solid-liquid separator to which the mother liquor is separated, and the concentrated acrylic acid solution is introduced to a crystallizer of a stage downstream of the solid-liquid separator to which the concentrated acrylic acid solution is separated, and the crystallization of the last stage among the two or more crystallization units A method for producing acrylic acid is provided, wherein purified acrylic acid is obtained from a solid-liquid separator of a unit, and a first crystallization unit among the two or more crystallization units includes a crystallizer having a crystallization temperature of -20 to -10°C.

[0012] According to the method for producing acrylic acid of the present invention, by crystallizing acrylic acid contained in an acrylic acid solution through a multi-stage crystallization process in which crystallization units are connected in multiple stages, acrylic acid can be obtained with high purity, and the final yield of acrylic acid can also be improved.

[0013] In particular, by controlling the crystallization temperature in the crystallizer of the first stage crystallization unit among two or more crystallization units to -20 to -10°C, the amount of acrylic acid crystallized in the crystallizer of the first stage crystallization unit can be the highest. Through this, the amount of mother liquor separated in the solid-liquid separator of the first stage crystallization unit can be reduced, and when some of the mother liquor separated from the first stage crystallization unit is circulated to the mother liquor treatment process, the amount of mother liquor that must be treated in the mother liquor treatment process is small, which can be preferable in terms of energy or economy. In addition, as the amount of acrylic acid crystallized increases, the final yield of purified acrylic acid can be satisfied.

[0014] Figure 1 is a process diagram showing a multi-stage crystallization process among the methods for producing acrylic acid according to one embodiment of the present invention.

[0015] Figures 2 to 4 are process diagrams showing a multi-stage crystallization process among the methods for manufacturing acrylic acid according to comparative examples.

[0016] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0017] Hereinafter, the present invention will be described in more detail.

[0018] In the present invention, the term "stream" may refer to the flow of fluid within a process, and may also refer to the fluid itself flowing within a moving line (pipe). Specifically, the "stream" may refer to both the fluid itself flowing within the pipe connecting each device and the flow of the fluid. In addition, the fluid may refer to one or more of gas, liquid, and solid.

[0019] According to one embodiment of the present invention, a method for producing acrylic acid comprises a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series, and acrylic acid contained in an acrylic acid solution introduced into the crystallizer of each stage is crystallized in the crystallizer of each stage to obtain a suspension including acrylic acid crystals, and the suspension is supplied to the solid-liquid separator of each stage, and the suspension is solid-liquid separated in the solid-liquid separator of each stage to obtain a concentrated acrylic acid solution and a mother liquor, wherein the mother liquor is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream is circulated to a crystallizer or a mother liquor treatment process of a stage upstream of the solid-liquid separator to which the mother liquor is separated, and the second mother liquor stream is circulated to a crystallizer of a stage to which the solid-liquid separator to which the mother liquor is separated, and the concentrated acrylic acid solution is introduced to a crystallizer of a stage downstream of the solid-liquid separator to which the concentrated acrylic acid solution is separated, and a solid-liquid stream of the last crystallization unit among the two or more crystallization units is separated. Purified acrylic acid is obtained from a separator, and the two or more crystallization units may include a crystallizer having a crystallization temperature of -20 to -10°C.

[0020] A method for producing acrylic acid according to one embodiment of the present invention can be performed by including a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series.

[0021] Specifically, the multi-stage crystallization process may be performed by including a multi-stage crystallizer in which two or more crystallization units are connected in multiple stages, and the crystallization process performed in each stage of the crystallization unit may be performed continuously. Each of the crystallization units may include a crystallizer and a solid-liquid separator, respectively.

[0022] The above crystallizer may be a device that crystallizes a specific substance into a solid by utilizing the difference in solubility of the substance according to temperature in a liquid mixture, and the solid-liquid separator may be a device that separates a solid-liquid mixture supplied to the solid-liquid separator into a solid phase and a liquid phase.

[0023] Meanwhile, when crystallization of an acrylic acid solution is performed using a single crystallization process, acrylic acid crystals cannot be obtained with the desired purity using only the single crystallization process because the content of impurities in the acrylic acid solution is high.

[0024] However, as in the present invention, when the crystallization process is performed in multiple stages, the acrylic acid solution is concentrated and crystallized in multiple stages, thereby satisfying the final yield of acrylic acid while improving the purity of the acrylic acid.

[0025] According to one embodiment of the present invention, a method for producing acrylic acid comprises crystallizing acrylic acid contained in an acrylic acid solution introduced into a crystallizer of each stage in a crystallizer of each stage to obtain a suspension containing acrylic acid crystals, and supplying the suspension to a solid-liquid separator of each stage.

[0026] Specifically, the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit among the crystallizers of each stage may be a crude acrylic acid aqueous solution containing crude acrylic acid. In this case, the crude acrylic acid may be acrylic acid before crystallization. Meanwhile, the first stage crystallization unit may be a crystallization unit located at the frontmost stage among the two or more crystallization units, and may be a single crystallizer to which the crude acrylic acid aqueous solution is introduced.

[0027] The above crude acrylic acid aqueous solution can be prepared as follows.

[0028] First, a reactant including a gas containing oxygen and a raw material compound is supplied to a reactor equipped with a catalyst, and a gas phase oxidation reaction is performed in the reactor in the presence of a catalyst to obtain a mixed gas containing acrylic acid. At this time, the acrylic acid may be crude acrylic acid, and the oxygen-containing gas may be air.

[0029] The above raw material compound may be at least one compound selected from the group consisting of propane, propylene, butane, i-butylene, t-butylene, and acrolein, and specifically, the raw material compound may include propylene.

[0030] Therefore, the mixed gas containing acrylic acid of the present invention may be a reaction product resulting from a gas phase oxidation reaction of reactants containing air and raw material compounds within the reactor. Specifically, the mixed gas may include acrylic acid, unreacted raw material compounds, acrolein, inert gases, carbon monoxide, carbon dioxide, and various organic by-products (such as acetic acid, low boiling point by-products, and high boiling point by-products). Here, the term "low boiling point by-products" (light ends) or "high boiling point by-products" (heavies) refers to a type of by-product that may be generated in the manufacturing process of the desired acrylic acid, and may be a compound having a molecular weight smaller or larger than that of acrylic acid.

[0031] The acrylic acid solution introduced into the crystallizer of the first stage crystallization unit may be obtained by contacting a mixed gas containing acrylic acid with an absorption solvent.

[0032] Specifically, an acrylic acid solution can be obtained through an absorption process in which a mixed gas containing the acrylic acid is brought into contact with water, which is an absorption solvent. At this time, considering the efficiency of the absorption process, the mixed gas can be supplied to the lower portion of the absorption tower where the absorption process is performed, and the absorption solvent, specifically water, can be supplied to the upper portion of the absorption tower.

[0033] In this way, the acrylic acid solution obtained by the above absorption process, i.e., the crude acrylic acid aqueous solution, can be introduced into the crystallizer of the first stage crystallization unit to perform the crystallization process.

[0034] According to the present invention, the content of acrylic acid contained in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit may be 80 to 95 wt%, and specifically, 82 to 90 wt%. Depending on the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit, the temperature at which acrylic acid is crystallized in the crystallizer of each stage and the amount of acrylic acid crystals produced depending on the temperature may vary.

[0035] More specifically, when the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit is less than 80 wt%, since the content of acrylic acid in the acrylic acid solution is low, when the acrylic acid solution is supplied to the crystallizer, the amount of acrylic acid crystals obtained by crystallization may also be low, and the process performed to satisfy the purity and yield of acrylic acid at the desired level in the present invention may become complicated. On the other hand, when the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit exceeds 95 wt%, an additional purification process may be required to obtain such an acrylic acid solution, and this may be undesirable from the economical viewpoint such as the process equipment cost and device cost for performing the purification process. In addition, when performing the purification process, energy consumption may increase excessively.

[0036] Meanwhile, as described above, the crude acrylic acid aqueous solution obtained as described above can be introduced into the crystallizer of the first stage crystallization unit as an acrylic acid solution. Meanwhile, the concentrated acrylic acid solution separated in the solid-liquid separator described below, specifically, the solid-liquid separator of the previous stage, can be introduced into the crystallizer of the crystallization unit subsequent to the first stage crystallization unit, i.e., the crystallizer of the crystallization unit from the second stage onwards, as the acrylic acid solution.

[0037] Here, the crystallization unit subsequent to the first stage crystallization unit may refer to all crystallization units subsequent to the first stage crystallization unit among the two or more crystallization units. For example, if the crystallization units are four stages in total, the crystallization units subsequent to the first stage crystallization unit may be the second stage crystallization unit, the third stage crystallization unit, and the fourth stage crystallization unit.

[0038] Accordingly, as the crystallization unit following the first stage crystallization unit moves to the later stage, the content of acrylic acid included in the concentrated acrylic acid solution introduced into the crystallizer of each crystallization unit may increase.

[0039] Meanwhile, the acrylic acid contained in the acrylic acid solution is crystallized through the crystallization process performed in each of the above-described crystallizers, thereby obtaining a suspension containing acrylic acid crystals. Thereafter, the suspension obtained from each of the above-described crystallizers can be supplied to the solid-liquid separator of the stage to which the crystallizer from which the suspension was obtained belongs.

[0040] According to one embodiment of the present invention, the mass ratio of the acrylic acid crystals contained in the suspension discharged from the crystallizer of each stage to the mass of the suspension may be 10 to 40 wt%, and specifically 20 to 35 wt%. The mass ratio of the acrylic acid crystals contained in the suspension to the total mass of the suspension discharged from the crystallizer of each stage may have the same meaning as the mass flow rate ratio of the crystallized acrylic acid contained in the suspension to the mass flow rate of the suspension supplied to the solid-liquid separator of each stage.

[0041] More specifically, when the mass ratio of the acrylic acid crystals contained in the suspension compared to the mass of the suspension discharged from the crystallizer of each stage, i.e., the concentration of the acrylic acid crystals in the suspension (Acrylic Acid Crystal Content) is less than 10 wt%, a relatively small amount of acrylic acid is crystallized in the crystallizer of each stage, and therefore, in order to meet the desired level of acrylic acid production, the total number of times and the throughput of the multi-stage crystallization process may be increased. When the concentration of the acrylic acid crystals in the suspension exceeds 40 wt%, the content of the solid acrylic acid crystals in the suspension increases, and thus, stirring of the suspension may be difficult inside the crystallizer of each stage. Accordingly, it may also be difficult to move the suspension to a solid-liquid separator, and thus, it may be difficult to perform the crystallization process.

[0042] According to a method for producing acrylic acid according to one embodiment of the present invention, the suspension is subjected to solid-liquid separation in a solid-liquid separator of each stage to obtain a concentrated acrylic acid solution and a mother liquor. Specifically, in the solid-liquid separator of each stage, the suspension obtained in the crystallizer of each stage is subjected to solid-liquid separation to obtain acrylic acid crystals in a solid phase and a mother liquor in a liquid phase. The mother liquor may be the remainder after the acrylic acid crystals are separated from the suspension, and may include acrylic acid, water, and acetic acid that have not been crystallized.

[0043] Furthermore, the concentrated acrylic acid may be obtained by subjecting the suspension to solid-liquid separation in the solid-liquid separator of each stage to obtain acrylic acid crystals and melting the acrylic acid crystals. That is, the concentrated acrylic acid solution may be obtained by melting the acrylic acid crystals with heat. For example, the molten acrylic acid crystals may be introduced into a subsequent crystallizer as the concentrated acrylic acid solution.

[0044] More specifically, the melting may be a physical process of phase transition from a solid to a liquid, and even if the melting of the acrylic acid crystals is performed, the mole number of acrylic acid contained in the acrylic acid crystals may not change. At this time, a separate heat supply device, for example, a heat exchanger, may be additionally provided to melt the acrylic acid crystals. The concentrated acrylic acid solution may include acrylic acid, and in addition, may include impurities (water, acetic acid, etc.) contained in the acrylic acid crystals and a trace amount of mother liquor that was not separated in the solid-liquid separator of each stage and remained in the acrylic acid crystals.

[0045] It may be desirable to melt the acrylic acid crystals separated from the solid-liquid separator of the above two or more crystallization units in order to introduce them into the crystallizer of the subsequent crystallization unit of the stage to which the solid-liquid separator from which the acrylic acid crystals were separated belongs or to obtain them as a product. That is, the melting of the acrylic acid crystals may be performed to move the acrylic acid crystals within the multi-stage crystallization process because the acrylic acid crystals are in a solid phase.

[0046] According to a method for producing acrylic acid according to one embodiment of the present invention, the mother liquor is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream is circulated to a crystallizer or mother liquor treatment process of a stage before the solid-liquid separator from which the mother liquor is separated, and the second mother liquor stream can be circulated to a crystallizer of a stage before the solid-liquid separator from which the mother liquor is separated.

[0047] Specifically, the mother liquor is separated from the solid-liquid separator of each stage, and can be branched into a first mother liquor stream and a second mother liquor stream.

[0048] Thereafter, the first mother liquor stream may be circulated to a crystallizer in a stage preceding the mother liquor treatment process or the stage to which the solid-liquid separator from which the first mother liquor stream originated belongs. Specifically, the first mother liquor stream branched from the mother liquor obtained from the solid-liquid separator of the first-stage crystallization unit may be circulated to the mother liquor treatment process. Meanwhile, the first mother liquor stream branched from the mother liquor obtained from the solid-liquid separator of the crystallization unit subsequent to the first-stage crystallization unit may be circulated to a crystallizer in a stage preceding the solid-liquid separator from which the mother liquor was obtained belongs.

[0049] According to the present invention, the mother liquor treatment process may be performed by including at least one of a purge process and an acrylic acid purification process. Specifically, the mother liquor treatment process may be a process for treating a first mother liquor stream among the mother liquors separated in the solid-liquid separator of the first stage crystallization unit.

[0050] More specifically, the purging may be performed when the content of acrylic acid in the first mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit is relatively low, and may be a process for discharging the first mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit to the outside of the system and discarding it.

[0051] Meanwhile, the acrylic acid purification process may be performed when the content of acrylic acid in the first mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit is relatively high, and may be a process of separating acrylic acid by distilling the first mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit.

[0052] Meanwhile, the second mother liquor stream can be circulated to the crystallizer of the stage to which the solid-liquid separator from which the second mother liquor stream is branched belongs.

[0053] According to one embodiment of the present invention, the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream may be 0.5:9.5 to 9.5:0.5, specifically, 1:9 to 9:1. The mass flow rate ratio of the first mother liquor stream and the second mother liquor stream may refer to the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of each stage. By controlling the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream within the above range, the concentration of the acrylic acid crystals in the suspension described above can be adjusted to 10 to 40 wt%. Through this, the fluidity of the suspension can be further maximized, and the flowability of the stream can be made flexible when performing a crystallization process performed in multiple stages.

[0054] According to a method for producing acrylic acid according to one embodiment of the present invention, the concentrated acrylic acid solution can be introduced into a crystallizer at a subsequent stage of a solid-liquid separator in which the concentrated acrylic acid solution is separated.

[0055] Specifically, the concentrated acrylic acid solution is obtained by melting the acrylic acid crystals separated from the solid-liquid separator of each stage. The concentrated acrylic acid solution can be introduced into a crystallizer located at a subsequent stage of the solid-liquid separator from which the concentrated acrylic acid solution was separated. Accordingly, as described above, the concentrated acrylic acid solution can be introduced as an acrylic acid solution into the crystallizer of a crystallization unit subsequent to the first stage crystallization unit.

[0056] For example, if there are three crystallization units in total, the concentrated acrylic acid solution separated in the solid-liquid separator of the second-stage crystallization unit can be introduced into the crystallizer of the third-stage crystallization unit.

[0057] According to a method for producing acrylic acid according to one embodiment of the present invention, purified acrylic acid can be obtained from a solid-liquid separator of the last crystallization unit among the two or more crystallization units.

[0058] As described above, the acrylic acid crystals separated from the solid-liquid separator of each stage are melted to obtain a concentrated acrylic acid solution, and the concentrated acrylic acid solution can be introduced to a crystallizer at the rear stage of the solid-liquid separator from which the concentrated acrylic acid solution originated.

[0059] However, since the latter crystallization unit does not exist and acrylic acid must be finally obtained, the acrylic acid crystals separated from the solid-liquid separator of the latter crystallization unit can be melted to obtain purified acrylic acid, which is the product of the present invention. The latter crystallization unit may refer to a crystallization unit located at the rearmost end of two or more crystallization units connected in multiple stages.

[0060] According to the method for producing acrylic acid of the present invention, the first stage crystallization unit among the two or more crystallization units may include a crystallizer having a crystallization temperature of -20 to -10°C. At this time, the crystallization temperature may refer to an operating temperature of the crystallizer for crystallizing the acrylic acid solution introduced into the crystallizer of each stage into acrylic acid crystals. When the crystallization temperature in the crystallizer included in the first stage crystallization unit is within the above range, the yield of acrylic acid in the crystallizer of the first stage crystallization unit may be the highest. At this time, the yield of acrylic acid may refer to the mass of acrylic acid crystallized in the crystallizer of each stage relative to the mass of acrylic acid included in the acrylic acid solution introduced into the crystallizer of each stage.

[0061] Through this, the amount of mother liquor separated in the solid-liquid separator of the first stage crystallization unit can be reduced, and it may be desirable from an economic or energy consumption perspective to circulate some of this small amount of mother liquor to the mother liquor treatment process. For example, when purging a large amount of mother liquor, the cost of loss of acrylic acid contained in the mother liquor may be excessively incurred, and when circulating a large amount of mother liquor to the acrylic acid purification process, the energy used to purify a large amount of mother liquor in the acrylic acid purification process may significantly increase. Therefore, it may be desirable to reduce the amount of mother liquor circulated to the mother liquor treatment process.

[0062] In addition, by melting the acrylic acid crystals separated from the solid-liquid separator of the first stage crystallization unit and introducing them into a crystallizer of a subsequent crystallization unit of the first stage crystallization unit to perform a multi-stage crystallization process, it is possible to obtain purified acrylic acid with high purity while satisfying the final yield of acrylic acid. At this time, the final yield of acrylic acid may mean the mass ratio of acrylic acid contained in the concentrated acrylic acid solution separated from the solid-liquid separator of the subsequent crystallization unit to the mass of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit.

[0063] Hereinafter, a process that can be included in an embodiment of the present invention will be described with reference to FIG. 1.

[0064] According to one embodiment of the present invention, the two or more crystallization units are two stages in total, and the crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be -20 to -10°C, and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit may be 0 to 12°C. Specifically, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be -14 to -9°C, and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit may be 4 to 9°C.

[0065] More specifically, the lower the crystallization temperature in the crystallizer (a) of the first stage crystallization unit, the more the yield of acrylic acid in the crystallizer (a) of the first stage crystallization unit can be maximized. However, since crystals of acrylic acid and water are simultaneously generated at a temperature below the eutectic point of acrylic acid and water, it may be preferable that the crystallization temperature in the crystallizer (a) of the first stage crystallization unit be performed at a temperature higher than the eutectic point. Accordingly, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be a temperature close to the eutectic point of acrylic acid and water contained in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit, but may also be a temperature higher than the eutectic point, when the content of acrylic acid contained in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit is 80 to 95 wt%.

[0066] Furthermore, when the crystallization temperature in the crystallizer (a) of the first stage crystallization unit is within the above range, the yield of acrylic acid may be the highest in the crystallizer (a) of the first stage crystallization unit. This is because the closer the crystallization temperature is to the eutectic point, the mass of the solid produced in the crystallizer may increase compared to the liquid. In this way, a large number of acrylic acid crystals are produced in the crystallizer (a) of the first stage crystallization unit, and by melting them and performing a multi-stage crystallization process through a crystallization unit subsequent to the first stage crystallization unit, the final yield of purified acrylic acid may increase.

[0067] Meanwhile, when the crystallization temperature in the crystallizer (a) of the second stage crystallization unit is within the above range, the first and second mother liquor streams branched from the solid-liquid separator (b) of the second stage crystallization unit are supplied to the crystallizers (a) of the first and second stage crystallization units, respectively, so that the concentration of the suspended acrylic acid crystals discharged from the crystallizers (a) of the first and second stage crystallization units can be controlled to 10 to 40 wt%. In addition, it may be desirable to control the crystallization temperature in the crystallizer of the second stage crystallization unit within the above range in terms of the use of a coolant (utility) for the crystallization process and the purity of acrylic acid.

[0068] According to one embodiment of the present invention, the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the first stage crystallization unit may be 0.5:9.5 to 1:1, and the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the second stage crystallization unit may be 1:1 to 9:1. In this case, the concentration of the suspended acrylic acid crystals discharged from the crystallizer (a) of each stage may be controlled to 10 to 40 wt%. Through this, when performing the multi-stage crystallization process, the flow of the stream within the crystallization unit or between the crystallization units may be performed continuously. At this time, the stream may include, for example, a suspension.

[0069] The ranges of the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the first stage crystallization unit and the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the second stage crystallization unit may be determined according to the crystallization temperature in the crystallizer (a) of each stage and the content of acrylic acid crystals contained in the suspension discharged from the crystallizer (a) of each stage. Accordingly, the mass flow rate ratios in the first and second stage crystallization units may be mass flow rate ratios that are controlled when the crystallization temperature in the crystallizer (a) of the first stage crystallization unit is -20 to -10°C and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit is 0 to 12°C.

[0070] In one embodiment, the first stage crystallization unit may include an auxiliary crystallizer arranged upstream of the crystallizer. Specifically, the auxiliary crystallizer may be a separate device from the crystallizer, and the auxiliary crystallizer and the crystallizer may be connected to each other. For example, the acrylic acid solution, i.e., a crude acrylic acid aqueous solution, may be supplied to the auxiliary crystallizer, and a suspension obtained from the auxiliary crystallizer may be supplied to a crystallizer connected subsequently from the auxiliary crystallizer.

[0071] When the crystallization unit of the first stage further includes the auxiliary crystallizer, a temperature gradient can be applied through the auxiliary crystallizer and the crystallizer to perform a crystallization process in the crystallization unit of the first stage.

[0072] Specifically, the crystallization temperature in the auxiliary crystallizer may be -5 to 5°C. More specifically, when the crystallization temperature in the auxiliary crystallizer is within the above range, the temperature of the crude acrylic acid aqueous solution supplied to the auxiliary crystallizer and the crystallization temperature in the auxiliary crystallizer may not differ drastically. This may be preferable in terms of the purity of the acrylic acid crystals produced.

[0073] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and the scope of the present invention is not limited to these examples alone.

[0074] Example

[0075] Example 1

[0076] The acrylic acid manufacturing process was simulated using the Aspen Plus simulator from Aspen, Inc., according to the process diagram shown in Fig. 1. The crystallizer model was used, which reflected the SLE (Solid-Liquid Equillibrium) data of acrylic acid and water, acrylic acid and acetic acid, and water and acetic acid, as well as the distribution coefficient values ​​of water and acetic acid from the crystallization experiment results of acrylic acid, water, and acetic acid.

[0077] Specifically, an acrylic acid solution containing acrylic acid (85 wt%), acetic acid (3 wt%), and water (12 wt%) was prepared, and the acrylic acid solution was introduced into a multi-stage crystallization process in which two stages of crystallization units were connected.

[0078] Specifically, the acrylic acid solution was supplied to the crystallizer (a) of the first stage crystallization unit and a crystallization process was performed. Through this, a suspension containing acrylic acid crystals was obtained. At this time, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit was -13°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first stage crystallization unit was 30 wt%.

[0079] Thereafter, the suspension obtained from the crystallizer (a) of the first stage crystallization unit was supplied to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained from the crystallizer (a) of the first stage crystallization unit was separated into acrylic acid crystals and mother liquor. At this time, the solid-liquid separator (b) of the first stage crystallization unit performed solid-liquid separation of the suspension through filtration.

[0080] The mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit was divided into a first mother liquor stream and a second mother liquor stream, and circulated to the mother liquor treatment process and the crystallizer (a) of the first stage crystallization unit, respectively. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream divided from the solid-liquid separator (b) of the first stage crystallization unit was 1.2:8.8.

[0081] Meanwhile, the acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit were melted to obtain a concentrated acrylic acid solution. The concentrated acrylic acid solution derived from the solid-liquid separator (b) of the first stage crystallization unit was supplied to the crystallizer (a) of the second stage crystallization unit.

[0082] Through a crystallization process performed in the crystallizer (a) of the second stage crystallization unit, a suspension containing acrylic acid crystals was obtained. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was 8°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30 wt%.

[0083] Thereafter, the suspension obtained from the crystallizer (a) of the second stage crystallization unit was supplied to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained from the crystallizer (a) of the second stage crystallization unit was separated into acrylic acid crystals and mother liquor. At this time, the solid-liquid separator (b) of the second stage crystallization unit performed solid-liquid separation of the suspension through filtration.

[0084] The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was divided into a first mother liquor stream and a second mother liquor stream and circulated to the crystallizers (a) of the first stage crystallization unit and the second stage crystallization unit, respectively. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream divided from the solid-liquid separator (b) of the second stage crystallization unit was 6.7:3.3.

[0085] Meanwhile, a concentrated acrylic acid solution was obtained by melting the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit as purified acrylic acid.

[0086] As a result, the purified acrylic acid contained acrylic acid (99.0 wt%), acetic acid (0.61 wt%), and water (0.37 wt%). In addition, the mass ratio of the acrylic acid contained in the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit to the mass of the acrylic acid contained in the acrylic acid solution supplied to the crystallizer (a) of the first stage crystallization unit, i.e., the final yield of acrylic acid, was 69.8%.

[0087] Example 2

[0088] In the above Example 2, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was -2°C compared to Example 1, the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit was 2.4:7.6, and the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the second stage crystallization unit was 0.5:9.5.

[0089] As a result, the purified acrylic acid contained acrylic acid (97.5 wt%), acetic acid (1.2 wt%), and water (1.3 wt%), and the final yield of acrylic acid was 72.5%.

[0090] Comparative example

[0091] Comparative Example 1

[0092] According to the process diagram shown in Fig. 2, the manufacturing process of acrylic acid was simulated using the Aspen Plus simulator from Aspen.

[0093] In Comparative Example 1, the mother liquor separated in the solid-liquid separator (b) of the first stage crystallization unit and the second stage crystallization unit was not branched, and the mother liquor was supplied to the mother liquor treatment process and the crystallizer (a) of the first stage crystallization unit, respectively.

[0094] Specifically, an acrylic acid solution prepared with the same composition as in Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit to obtain a suspension containing acrylic acid crystals. The acrylic acid solution had the same composition as in Example 1. The crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -0.2°C. The suspension obtained from the crystallizer (a) of the first-stage crystallization unit was supplied to the solid-liquid separator (b) of the first-stage crystallization unit. At this time, the mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second-stage crystallization unit was 30 wt%.

[0095] In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained from the crystallizer (a) of the first stage crystallization unit was separated into acrylic acid crystals and a mother liquor. At this time, the solid-liquid separator (b) of the first stage crystallization unit performed solid-liquid separation of the suspension through filtration. The acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit were melted to obtain a concentrated acrylic acid solution. The concentrated acrylic acid solution derived from the solid-liquid separator (b) of the first stage crystallization unit was supplied to the crystallizer (a) of the second stage crystallization unit, and the mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit was introduced into a mother liquor treatment process.

[0096] In the crystallizer (a) of the second stage crystallization unit, the concentrated acrylic acid solution derived from the solid-liquid separator (b) of the first stage crystallization unit was crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was 11.1°C.

[0097] The suspension obtained from the crystallizer (a) of the second stage crystallization unit was supplied to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained from the crystallizer (a) of the second stage crystallization unit was separated into acrylic acid crystals and a mother liquor. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, solid-liquid separation of the suspension was performed through filtration. The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was supplied to the crystallizer (a) of the first stage crystallization unit. A concentrated acrylic acid solution obtained by melting the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit was obtained as purified acrylic acid.

[0098] As a result, the purified acrylic acid contained acrylic acid (99.6 wt%), acetic acid (0.29 wt%), and water (0.15 wt%), and the final yield of the final acrylic acid was 13.8%.

[0099] In the above comparative example 1, the mother liquor separated from the solid-liquid separator of the first and second stage crystallization units was not branched compared to the example, and it was confirmed that the final yield of acrylic acid was the lowest.

[0100] Comparative Example 2

[0101] In Comparative Example 2, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit was -4.5°C compared to Comparative Example 1, and the mass ratio of acrylic acid crystals contained in the suspension discharged from the crystallizer (a) of the first stage crystallization unit to the mass of the suspension was 50 wt%.

[0102] As a result, mixing was not performed in the crystallizer (a) of the first stage crystallization unit, so the crystallization process could not be performed and acrylic acid could not be obtained.

[0103] Comparative Example 3

[0104] According to the process diagram shown in Fig. 3, the manufacturing process of acrylic acid was simulated using the Aspen Plus simulator from Aspen.

[0105] Specifically, an acrylic acid solution having the same composition as Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit. The acrylic acid solution was crystallized in the crystallizer (a) of the first-stage crystallization unit to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -2.6°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first-stage crystallization unit was 30 wt%.

[0106] The suspension obtained from the crystallizer (a) of the first stage crystallization unit was supplied to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained from the crystallizer (a) of the first stage crystallization unit was separated into acrylic acid crystals and a mother liquor. At this time, in the solid-liquid separator (b) of the first stage crystallization unit, solid-liquid separation of the suspension was performed through filtration. Meanwhile, the acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit were melted to obtain a concentrated acrylic acid solution.

[0107] The mother liquor separated in the solid-liquid separator (b) of the first stage crystallization unit was supplied to the crystallizer (a) of the second stage crystallization unit and crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was -7.7°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30 wt%.

[0108] The suspension obtained from the crystallizer (a) of the second stage crystallization unit was supplied to the solid-liquid separator (b) of the second stage crystallization unit, thereby separating the acrylic acid crystals and the mother liquor. At this time, the solid-liquid separator (b) of the second stage crystallization unit performed solid-liquid separation of the suspension through filtration. The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was discharged.

[0109] Meanwhile, the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit were melted to obtain a concentrated acrylic acid solution, and the concentrated acrylic acid solution separated from the solid-liquid separator (b) of the second stage crystallization unit was mixed with the concentrated acrylic acid solution separated from the solid-liquid separator (b) of the first stage crystallization unit to form a mixed stream, and the mixed stream was obtained as purified acrylic acid.

[0110] The above purified acrylic acid contained acrylic acid (97.1 wt%), acetic acid (1.1 wt%), and water (1.7 wt%), and the final yield of acrylic acid was 59.6%.

[0111] As a result, it was confirmed that the purity of purified acrylic acid and the final yield of acrylic acid in Comparative Example 3 were reduced compared to the Examples.

[0112] Comparative Example 4

[0113] According to the process diagram shown in Fig. 4, the manufacturing process of acrylic acid was simulated using Aspen Plus simulator from Aspen.

[0114] Specifically, an acrylic acid solution having the same composition as Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit. The acrylic acid solution was crystallized in the crystallizer (a) of the first-stage crystallization unit to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -3.0°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first-stage crystallization unit was 30 wt%.

[0115] The suspension obtained from the crystallizer (a) of the first stage crystallization unit was supplied to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained from the crystallizer (a) of the first stage crystallization unit was separated into acrylic acid crystals and a mother liquor. At this time, in the solid-liquid separator (b) of the first stage crystallization unit, solid-liquid separation of the suspension was performed through filtration. Meanwhile, the acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit were melted to obtain a concentrated acrylic acid solution.

[0116] The mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit was branched into a first mother liquor stream and a second mother liquor stream and circulated to the crystallizer (a) of the first stage crystallization unit and the crystallizer (a) of the second stage crystallization unit, respectively. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the first stage crystallization unit was 0.9:9.1.

[0117] Through a crystallization process performed in the crystallizer (a) of the second stage crystallization unit, a suspension containing acrylic acid crystals was obtained. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was -13°C. The mass ratio of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30 wt%.

[0118] Thereafter, the suspension obtained from the crystallizer (a) of the second stage crystallization unit was supplied to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained from the crystallizer (a) of the second stage crystallization unit was separated into acrylic acid crystals and a mother liquor. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, solid-liquid separation of the suspension was performed through filtration. Meanwhile, the acrylic acid crystals separated in the solid-liquid separator (b) of the second stage crystallization unit were melted to obtain a concentrated acrylic acid solution.

[0119] The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was branched into a first mother liquor stream and a second mother liquor stream, and supplied to the crystallizer (a) of the second stage crystallization unit and the outside of the system, respectively. At this time, the mass flow rate ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator (b) of the second stage crystallization unit was 1:1.

[0120] Meanwhile, the concentrated acrylic acid solution separated from the solid-liquid separator (b) of the second stage crystallization unit formed a mixed stream with the concentrated acrylic acid solution separated from the solid-liquid separator (b) of the first stage crystallization unit, and the mixed stream was obtained as purified acrylic acid.

[0121] The above purified acrylic acid contained acrylic acid (96.6 wt%), acetic acid (1.3 wt%), and water (2.1 wt%), and the final yield of acrylic acid was 73.6%.

[0122] As a result, it was confirmed that Comparative Example 4 had the lowest purity of the purified acrylic acid, i.e., the content of acrylic acid contained in the purified acrylic acid.

[0123] Comparative Example 5

[0124] Comparative Example 5 was a crystallization temperature of -5°C in the crystallizer of the first stage crystallization unit compared to Example 1, and the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit was 4.4:5.6, and the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of the second stage crystallization unit was 2.5:7.5.

[0125] As a result, the purified acrylic acid contained acrylic acid (99.0 wt%), acetic acid (0.57 wt%), and water (0.38 wt%), and the final yield of acrylic acid was 45.8%.

[0126] In the above comparative example 5, the crystallization temperature in the crystallizer of the first stage crystallization unit was higher than in example 1, and it was confirmed that the purity of acrylic acid in the purified acrylic acid was the same as in example 1, but the final yield of acrylic acid was significantly reduced.

[0127] [Explanation of symbols]

[0128] (a): Crystallizer

[0129] (b): High-liquid separator

Claims

1. A multi-stage crystallization process is performed including two or more crystallization units including a crystallizer and a solid-liquid separator connected in series, In the crystallizer of each stage, the acrylic acid contained in the acrylic acid solution introduced into the crystallizer of each stage is crystallized to obtain a suspension containing acrylic acid crystals, and the suspension is supplied to the solid-liquid separator of each stage. In the solid-liquid separator of each stage, the above suspension is separated into solid and liquid to obtain a concentrated acrylic acid solution and mother liquor. The mother liquor is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream is circulated to a crystallizer or mother liquor treatment process of the stage in which the solid-liquid separator from which the mother liquor is separated belongs, and the second mother liquor stream is circulated to a crystallizer of the stage in which the solid-liquid separator from which the mother liquor is separated belongs, The above-mentioned concentrated acrylic acid solution is introduced into a crystallizer at the rear end of the solid-liquid separator from which the above-mentioned concentrated acrylic acid solution is separated. Purified acrylic acid is obtained from the solid-liquid separator of the last crystallization unit among the above two or more crystallization units, A method for producing acrylic acid, wherein the first crystallization unit among the two or more crystallization units includes a crystallizer having a crystallization temperature of -20 to -10°C.

2. In paragraph 1, A method for producing acrylic acid, wherein the content of acrylic acid contained in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit is 80 to 95 wt%.

3. In paragraph 1, A method for producing acrylic acid, wherein the mass ratio of acrylic acid crystals contained in the suspension discharged from each crystallizer of the above stages is 10 to 40 wt%.

4. In paragraph 1, A method for producing acrylic acid, wherein the mass flow ratio of the first mother liquor stream and the second mother liquor stream is 0.5:9.5 to 9.5:0.

5.

5. In paragraph 1, The above two or more crystallization units are two stages in total, The crystallization temperature in the crystallizer of the first stage crystallization unit is -20 to -10 ℃, A method for producing acrylic acid, wherein the crystallization temperature in the crystallizer of the second stage crystallization unit is 0 to 12°C.

6. In paragraph 5, The mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of the first stage crystallization unit is 0.5:9.5 to 1:1, A method for producing acrylic acid, wherein the mass flow ratio of the first mother liquor stream and the second mother liquor stream branched from the solid-liquid separator of the second stage crystallization unit is 1:1 to 9:

1.

7. In paragraph 1, A method for producing acrylic acid, wherein the first stage crystallization unit includes an auxiliary crystallizer arranged in front of the crystallizer.

8. In paragraph 7, A method for producing acrylic acid, wherein the crystallization temperature in the auxiliary crystallizer is -5 to 5°C.

9. In paragraph 1, The acrylic acid solution introduced into the crystallizer of the first stage crystallization unit is: A method for producing acrylic acid obtained by contacting a mixed gas containing acrylic acid with an absorption solvent.

10. In paragraph 9, A method for producing acrylic acid, wherein the mixed gas containing the acrylic acid is a reaction product obtained by subjecting a reactant containing a gas containing oxygen and a raw material compound to a gas phase oxidation reaction.

11. In paragraph 10, A method for producing acrylic acid, wherein the above raw material compound is at least one compound selected from the group consisting of propane, propylene, butane, i-butylene, t-butylene, and (meth)acrolein.

12. In paragraph 1, Obtaining the concentrated acrylic acid solution from the solid-liquid separator of each stage above is as follows: A method for producing acrylic acid, comprising: obtaining acrylic acid crystals by solid-liquid separation of the suspension in the solid-liquid separator of each stage, and melting the acrylic acid crystals to obtain the concentrated acrylic acid solution.

13. In paragraph 1, A method for producing acrylic acid, wherein the above mother liquor treatment process is performed by including at least one of a purge and an acrylic acid purification process.

Images