Method for preparing acrylic acid

Abstract

The present invention provides a method for preparing acrylic acid, comprising: contacting a mixed gas containing acrylic acid with water in an absorption tower to obtain an acrylic acid solution containing acrylic acid; and crystallizing the acrylic acid by a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series.

Description

Method for producing acrylic acid

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0126983, filed September 22, 2023, and Korean Patent Application No. 10-2024-0112157, filed August 21, 2024, 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 aqueous solution through an absorption process in which it comes into contact with an absorption solvent such as water in an absorption tower. In this case, if the absorption efficiency in the absorption process is poor, a large amount of acrylic acid may be lost to the upper portion of the absorption tower where the absorption process is performed.

[0007] Afterwards, it is common for processes such as crystallization, extraction, distillation, and purification to be performed as subsequent processes to obtain acrylic acid contained in the acrylic acid aqueous solution.

[0008] In order to obtain acrylic acid contained in the above acrylic acid solution, a crystallization process is sometimes performed. However, 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.

[0009] Therefore, there is an urgent need to introduce a technology that can obtain high-purity acrylic acid from the acrylic acid solution while reducing the amount of acrylic acid lost in the absorption process.

[0010] The problem to be solved in the present invention is to provide a method for producing acrylic acid capable of reducing the amount of acrylic acid lost in the absorption process while obtaining acrylic acid contained in the acrylic acid solution with high purity, in order to solve the problem mentioned in the background technology of the present invention.

[0011] According to one embodiment of the present invention for solving the above problem, the present invention provides a method for producing an acrylic acid solution comprising acrylic acid by contacting a mixed gas containing acrylic acid with water in an absorption tower, wherein the crystallization of the 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, wherein the acrylic acid solution is introduced into a crystallizer of a first-stage crystallization unit among the two or more crystallization units, and in the crystallizer of each stage, 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 a 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 branched into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream is circulated to a crystallizer of a stage preceding the solid-liquid separator to which the mother liquor is separated or to the absorption tower, and the second mother liquor stream is supplied to the crystallizer of the stage preceding the solid-liquid separator to which the mother liquor is separated or to the absorption tower, and the second mother liquor stream is supplied to the crystallizer of the stage preceding the solid-liquid separator to which the mother liquor is separated or to the absorption tower, and the second mother liquor stream is supplied to the crystallizer of the stage preceding the solid-liquid separator of the stage to which the solid-liquid separator of ... A method for producing acrylic acid is provided, wherein the mother liquor is circulated to a crystallizer of a stage to which a solid-liquid separator from which the mother liquor is separated belongs, the concentrated acrylic acid solution is introduced to a crystallizer of a stage subsequent to the solid-liquid separator from which the concentrated acrylic acid solution is separated, and acrylic acid crystals are obtained from the solid-liquid separator of the final crystallization unit among the two or more crystallization units.

[0012] According to the method for producing acrylic acid of the present invention, purified acrylic acid can be obtained with high purity 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 and performed.

[0013] In particular, when two or more crystallization units are two stages in total, by controlling the crystallization temperature in the crystallizer of the first stage crystallization unit to -9 to 5 ℃, the content and flow rate of acrylic acid contained in the first mother liquor stream branched from the first stage solid-liquid separator can be adjusted, thereby maintaining the absorption efficiency in the absorption tower similar to the conventional one. Furthermore, it may be preferable in terms of refrigerant use in the crystallizer, and the content of impurities contained in the purified acrylic acid finally obtained can be lowered, thereby obtaining the purified acrylic acid with high purity.

[0014] Figure 1 is a process diagram showing a method for manufacturing acrylic acid according to one embodiment of the present invention.

[0015] Figures 2 to 5 are process diagrams showing a method 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] 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.

[0018] The term "upper" as used herein, unless otherwise specified, refers to a point 0% to 10% in height downward from the top of the device, and may specifically refer to the top (top). In addition, the term "lower" refers to a point 90% to 100% in height downward from the top of the device, and may specifically refer to the bottom (bottom).

[0019] Additionally, the “pressure” referred to herein means gauge pressure measured under atmospheric pressure conditions.

[0020] Meanwhile, unless otherwise specified herein, the operating pressure of the column means the pressure at the top of the column, and the operating temperature of the column means the temperature at the bottom of the column.

[0021] According to one embodiment of the present invention, a method for producing acrylic acid comprises: contacting a mixed gas containing acrylic acid with water in an absorption tower to obtain an acrylic acid solution containing acrylic acid; crystallization of the 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; the acrylic acid solution is introduced into a crystallizer of a first-stage crystallization unit among the two or more crystallization units; crystallizing acrylic acid contained in the acrylic acid solution introduced into the crystallizer of each stage in the crystallizer of each stage to obtain a suspension containing acrylic acid crystals; supplying the suspension to a solid-liquid separator of each stage; and separating the suspension from solid to liquid in the solid-liquid separator of each stage to obtain a concentrated acrylic acid solution and a mother liquor; wherein the mother liquor is branched into a first mother liquor stream and a second mother liquor stream; the first mother liquor stream is circulated to a crystallizer or the absorption tower of a stage preceding the solid-liquid separator to which the mother liquor is separated; and the second mother liquor stream is a stream of a solid-liquid separator of the stage to which the mother liquor is separated. The concentrated acrylic acid solution is circulated to a crystallizer of the stage to which the solid-liquid separator belongs, and the concentrated acrylic acid solution is introduced to a crystallizer of the stage after the solid-liquid separator to which the concentrated acrylic acid solution belongs, and purified acrylic acid can be obtained from the solid-liquid separator of the final crystallization unit among the two or more crystallization units.

[0022] A method for producing acrylic acid according to one embodiment of the present invention can obtain an acrylic acid solution containing acrylic acid by contacting a mixed gas containing acrylic acid with water in an absorption tower.

[0023] First, the mixed gas containing the acrylic acid can be prepared as follows.

[0024] 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 the 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. The crude acrylic acid may be acrylic acid before crystallization.

[0025] 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.

[0026] 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. Thereafter, the mixed gas containing acrylic acid may be supplied to an absorption tower.

[0027] Specifically, the mixed gas containing the acrylic acid may be brought into contact with water in the absorption tower to obtain an acrylic acid solution. At this time, considering the efficiency of the absorption process, the mixed gas may be supplied to the lower portion of the absorption tower, and the absorption solvent, specifically water, may be supplied to the upper portion of the absorption tower.

[0028] Here, the type of the absorption tower may be determined by taking into account the contact efficiency of the mixed gas and the absorption solvent, and may be, for example, a packed column type absorption tower or a multistage tray type absorption tower. The packed column type absorption tower may have a filler such as a lashing ring, a pall ring, a saddle, a gauze, or a structured packing applied therein.

[0029] Meanwhile, the absorption tower can be operated under an internal pressure of 1 to 1.5 bar or 1 to 1.3 bar and an internal temperature of 50 to 120°C or 50 to 100°C, taking into account the condensation conditions of acrylic acid and the moisture content according to the saturated water vapor pressure.

[0030] In this way, through the absorption process performed in the absorption tower, a crude acrylic acid aqueous solution containing crude acrylic acid can be obtained as an acrylic acid solution.

[0031] Meanwhile, according to the method for producing acrylic acid of the present invention, crystallization of the acrylic acid 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.

[0032] Specifically, the multi-stage crystallization process may be one in which two or more crystallization units are connected in multiple stages, and the crystallization process performed in each stage of the crystallization unit is performed continuously. Each of the crystallization units of the stages may include a crystallizer and a solid-liquid separator, respectively.

[0033] 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 the temperature in the liquid mixture, and the solid-liquid separator may be a device that separates the solid-liquid mixture supplied to the solid-liquid separator into a solid phase and a liquid phase.

[0034] Meanwhile, according to the method for producing acrylic acid of the present invention, the acrylic acid solution can be introduced into a crystallizer of the first crystallization unit among the two or more crystallization units.

[0035] Specifically, the crude acrylic acid aqueous solution obtained from the absorption tower may be introduced as an acrylic acid solution into the crystallizer of the first crystallization unit among the two or more crystallization units. As described above, the crude acrylic acid aqueous solution may include crude acrylic acid, which is acrylic acid before crystallization.

[0036] 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.

[0037] 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 each 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.

[0038] 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. Meanwhile, 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. Therefore, it may not be desirable from an economical standpoint, such as in terms of process equipment costs and device costs for performing the purification process, and energy usage may also increase excessively.

[0039] According to the method for producing acrylic acid of the present invention, 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 containing acrylic acid crystals, and the suspension can be supplied to the solid-liquid separator of each stage, specifically, to the solid-liquid separator of the stage to which the crystallizer from which the suspension is obtained belongs.

[0040] More specifically, the crude acrylic acid aqueous solution obtained as described above may be introduced into the crystallizer of the first stage crystallization unit as the acrylic acid solution. Meanwhile, the concentrated acrylic acid solution separated in the solid-liquid separator of the previous stage may be introduced into the crystallizer of the crystallization unit subsequent to the first stage crystallization unit, i.e., the crystallization unit from the second stage onwards, as the acrylic acid solution. 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, when 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.

[0041] 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.

[0042] Meanwhile, through the crystallization process performed in the crystallizer of each stage, the acrylic acid contained in the acrylic acid solution is crystallized, thereby obtaining a suspension containing acrylic acid crystals. Thereafter, the suspension obtained from the crystallizer of each stage can be supplied to the solid-liquid separator of the stage to which the crystallizer in which the suspension was obtained belongs.

[0043] 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.

[0044] 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 satisfy 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.

[0045] According to the method for producing acrylic acid 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 liquid.

[0046] Specifically, in the solid-liquid separator of each stage, the suspension obtained from the crystallizer of each stage is subjected to solid-liquid separation, thereby obtaining solid acrylic acid crystals and a liquid mother liquor. The mother liquor may be the remainder from which the acrylic acid crystals are separated from the suspension, and may include uncrystallized acrylic acid, water, and acetic acid.

[0047] According to one embodiment of the present invention, obtaining the concentrated acrylic acid solution from the solid-liquid separator of each stage may be performed by including 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 to obtain the concentrated acrylic acid solution.

[0048] Specifically, in the solid-liquid separator of each stage, the suspension obtained from the crystallizer of each stage is subjected to solid-liquid separation, thereby obtaining solid acrylic acid crystals and a liquid mother liquor. The mother liquor may be the remainder from which the acrylic acid crystals are separated from the suspension, and may include uncrystallized acrylic acid, water, and acetic acid.

[0049] 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.

[0050] The above 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 contain acrylic acid, and in addition, may contain 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.

[0051] It may be desirable to melt the acrylic acid crystals separated from the solid-liquid separator of each stage above 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. That is, 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.

[0052] 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 of a prior-stage of a stage to which the solid-liquid separator from which the mother liquor is separated or to the absorption tower, and the second mother liquor stream can be circulated to a crystallizer of a stage to which the solid-liquid separator from which the mother liquor is separated is located.

[0053] 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.

[0054] Thereafter, the place where the first mother liquor stream is circulated may be the crystallizer in the front of the stage to which the absorption tower or the solid-liquid separator from which the first mother liquor stream is derived 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 absorption tower. 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 the crystallizer in the front of the stage to which the solid-liquid separator from which the mother liquor is obtained belongs.

[0055] 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 originated belongs.

[0056] According to one embodiment of the present invention, the mother liquor obtained from the solid-liquid separator of the first stage crystallization unit is branched into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream branched from the solid-liquid separator of the first stage can be circulated to the absorption tower, and the second mother liquor stream branched from the solid-liquid separator of the first stage can be circulated to the crystallizer of the first stage crystallization unit.

[0057] Specifically, the solid-liquid separator of the first stage may be a solid-liquid separator included in the first stage crystallization unit. The first mother liquor stream branched from the solid-liquid separator of the first stage may be circulated to the absorption tower as the first mother liquor stream, and the second mother liquor stream branched from the solid-liquid separator of the first stage may be circulated to the crystallizer of the first stage crystallization unit as the second mother liquor stream.

[0058] Meanwhile, the absorption efficiency in the absorption tower can be controlled depending on the flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage, the content of acrylic acid included in the first mother liquor stream branched from the solid-liquid separator of the first stage, and the position at which the first mother liquor stream branched from the solid-liquid separator of the first stage is circulated in the absorption tower.

[0059] Meanwhile, the content of acrylic acid included in the first mother liquid stream branched from the solid-liquid separator of the first stage may be 65 to 85 wt%, and specifically, may be 70 to 80 wt%.

[0060] Specifically, when the content of acrylic acid contained in the first mother liquor stream branched from the solid-liquid separator of the first stage is 85 wt% or less, the first mother liquor stream can serve as an absorption solvent for acrylic acid when introduced into the absorption tower. In addition, the higher the flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage and the lower the content of acrylic acid contained in the first mother liquor stream introduced into the absorption tower, the more the absorption efficiency in the absorption tower can be improved.

[0061] According to the present invention, the position at which the first mother liquor stream branched from the solid-liquid separator of the first stage is circulated to the absorption tower may be at a height of 10% to 60% downward from the top of the absorption tower, with the top of the absorption tower as 0%, and specifically, may be at a height of 20% to 50%.

[0062] If the position at which the first mother liquor stream branched from the solid-liquid separator of the first stage is circulated to the absorption tower is less than 10%, since the first mother liquor stream is circulated to a relatively high position, the first mother liquor stream having a relatively high content of acrylic acid is circulated to a position in the absorption tower where an absorption solution having a relatively low content of acrylic acid exists, which may reduce the absorption efficiency of the absorption tower. On the other hand, if the position at which the first mother liquor stream branched from the solid-liquid separator of the first stage is circulated to the absorption tower is more than 60%, since the first mother liquor stream is circulated to a relatively low position, an area within the absorption tower that can function as an absorption solvent to absorb acrylic acid contained in the mixed gas is reduced, which may make it difficult to function as an absorption solvent.

[0063] According to one embodiment of the present invention, the mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage may be 5 to 50% of the mass flow rate of the mixed gas containing the acrylic acid, and specifically, may be 5 to 30%.

[0064] Specifically, when the mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage is less than 5% of the mass flow rate of the mixed gas, the flow rate of the first mother liquor stream introduced into the absorption tower is relatively small, so it may be difficult to absorb acrylic acid contained in the mixed gas within the absorption tower. On the other hand, when the mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage exceeds 50% of the mass flow rate of the mixed gas, the size of the device, for example, the diameter of the absorption tower, must be increased, which may be undesirable from an economical point of view. In addition, the operating capacity of the absorption tower may exceed the design capacity, and in such a case, the operation of the absorption tower may become difficult.

[0065] 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 the after-stage of a solid-liquid separator in which the concentrated acrylic acid solution is separated.

[0066] 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 the subsequent stage of the solid-liquid separator from which the concentrated acrylic acid solution was separated. Therefore, as described above, the concentrated acrylic acid solution can be introduced as an acrylic acid solution into the crystallizer of the crystallization unit subsequent to the first stage crystallization unit.

[0067] 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.

[0068] 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.

[0069] Specifically, the concentrated acrylic acid solution obtained by melting the acrylic acid crystals separated from the solid-liquid separator of the final crystallization unit can be obtained as the product of the present invention, i.e., purified acrylic acid. The final crystallization unit may refer to a crystallization unit located at the rearmost stage among two or more crystallization units connected in multiple stages.

[0070] Hereinafter, a process that can be included in an embodiment of the present invention will be described with reference to FIG. 1.

[0071] According to one embodiment of the present invention, the two or more crystallization units are two stages in total,

[0072] The crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be -9 to 5°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 -8 to 0°C, and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit may be 5 to 10°C. At this time, the crystallization temperature may mean the operating temperature of the crystallizer for crystallizing the acrylic acid solution introduced into the crystallizer of each stage into acrylic acid crystals.

[0073] Specifically, when the two or more crystallization units are two stages in total, the crystallization unit may include a first stage crystallization unit and a second stage crystallization unit. The first stage crystallization unit is a crystallization unit including a crystallizer into which an acrylic acid solution obtained from an absorption tower is introduced, and the second stage crystallization unit is a crystallization unit subsequent to the first stage crystallization unit.

[0074] More specifically, when the crystallization temperature in the crystallizer (a) of the first stage crystallization unit is within the above range, since the crystallization temperature in the crystallizer of the first stage crystallization unit is relatively high and the amount of acrylic acid crystallized in the crystallizer (a) of the first stage crystallization unit is reduced, in order to achieve the production amount of acrylic acid targeted in the present invention, the flow rates of the acrylic acid solution introduced from the absorption tower (100) into the crystallizer (a) of the first stage crystallization unit and the mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit can be increased. Through this, the flow rate of the first mother liquor stream branched from the solid-liquid separator (b) of the first stage can also be increased, and the absorption efficiency in the absorption tower (100) can be increased as much as the flow rate of the first mother liquor stream circulated to the absorption tower increases. On the other hand, as the amount of acrylic acid crystallized in the crystallizer (a) of the first stage crystallization unit decreases, the composition of acrylic acid in the mother liquor separated in the solid-liquid separator (b) of the first stage crystallization unit may increase, and as the composition of acrylic acid in the first mother liquor stream branched from the solid-liquid separator (b) of the first stage increases, the absorption efficiency in the absorption tower (100) may decrease.

[0075] Therefore, when the crystallization temperature in the crystallizer (a) of the first stage crystallization unit is within the above range, the decrease in absorption efficiency due to the increase in the composition of acrylic acid in the first mother liquor stream branched from the solid-liquid separator (b) of the first stage and the increase in absorption efficiency through the increase in the flow rate of the first mother liquor stream may work together. In this case, the loss of acrylic acid in the absorption tower (100) may be maintained similar to that in the past, and since the temperature of the crystallizer (a) of the first stage crystallization unit is relatively high, there may be an advantage in terms of the use of a refrigerant (utility) for the crystallization process in the first stage crystallization unit. Furthermore, since the amount of impurities, such as acetic acid and water, concentrated together with acrylic acid in the crystallizer (a) of the first stage crystallization unit is reduced, it may be preferable in terms of the purity of the purified acrylic acid finally obtained.

[0076] Meanwhile, when the crystallization temperature range in the crystallizer (a) of the first stage crystallization unit is exceeded, the content of acrylic acid in the first mother liquor stream branched from the solid-liquid separator (b) of the first stage excessively increases, so that even if the flow rate of the first mother liquor stream branched from the solid-liquid separator (b) of the first stage is high, the loss of acrylic acid in the absorption tower (100) may increase.

[0077] Meanwhile, when the crystallization temperature in the crystallizer 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 acrylic acid crystals in the suspension discharged from the crystallizers of the first and second stage crystallization units can be maintained at 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.

[0078] 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 1:9 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 acrylic acid crystals in the suspension 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, thereby ultimately obtaining acrylic acid. At this time, the stream may include, for example, a suspension.

[0079] The range 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 can be determined according to the crystallization temperature in the crystallizer (a) of each stage and the concentration of acrylic acid crystals included in the suspension discharged from the crystallizer (a) of each stage.

[0080] 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.

[0081] Example

[0082] Example 1

[0083] 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.

[0084] Specifically, a mixed gas comprising acrylic acid (16.6 wt%), acetic acid (0.46 wt%), and water (6.96 wt%) was brought into contact with water as an absorption solvent in an absorption tower (100) to obtain an acrylic acid solution. The acrylic acid solution was introduced as a side discharge stream from the absorption tower into a multi-stage crystallization process in which a total of two stages of crystallization units were connected.

[0085] Meanwhile, the upper discharge stream of the absorption tower containing components not absorbed in the water was discharged outside the system, and the lower discharge stream of the absorption tower containing high-boiling-point by-products was supplied to the high-boiling-point by-product removal tower.

[0086] In the high-boiling-point by-product removal tower, the bottom discharge stream of the absorption tower was distilled, the high-boiling-point by-products were discharged outside the system, and the acrylic acid solution from which the high-boiling-point by-products were separated was mixed with the side discharge stream of the absorption tower to obtain a mixed stream. The mixed stream contained acrylic acid (88.8 wt%), acetic acid (2.98 wt%), and water (5.7 wt%).

[0087] Specifically, the above mixed stream 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 -2°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%.

[0088] 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.

[0089] The mother liquor separated in 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 absorption tower (100) and the crystallizer (a) of the first stage crystallization unit, respectively. At this time, the first mother liquor stream branched in the solid-liquid separator of the first stage was circulated downward at a height of 26% from the top of the absorption tower (100) based on 0% of the top of the absorption tower. In addition, the mass flow rate of the first mother liquor stream branched in the solid-liquid separator of the first stage was 16% of the mass flow rate of the mixed gas. The mass flow rate of the first mother liquor stream branched in the solid-liquid separator of the first stage was 99.2% of the mass flow rate of the acrylic acid crystals separated in the solid-liquid separator (b) of the second stage crystallization unit described below.

[0090] Meanwhile, 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 was 1.7:8.3. The first mother liquor stream branched from the solid-liquid separator of the first stage contained acrylic acid (78.2 wt%), acetic acid (5.5 wt%), and water (11.2 wt%).

[0091] 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.

[0092] 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 9.5°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%.

[0093] 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.

[0094] 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 circulated to the crystallizer of the first stage crystallization unit and the crystallizer 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 second stage crystallization unit was 6.7:3.3.

[0095] Meanwhile, purified acrylic acid was obtained from a concentrated acrylic acid solution obtained by melting acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit.

[0096] As a result, the purified acrylic acid contained acrylic acid (99.4 wt%), acetic acid (0.4 wt%), and water (0.1 wt%). In addition, the content of acrylic acid (acrylic acid loss) contained in the upper discharge stream of the absorption tower was 0.137 mol%. Here, the mol% of acrylic acid is a value expressed as a percentage of the ratio of the number of moles of acrylic acid to the total number of moles of the upper discharge stream (gas phase) of the absorption tower.

[0097] Example 2

[0098] In Example 2, the crystallization temperature in the crystallizer of the first stage crystallization unit was -5°C compared to Example 1, and the crystallization temperature in the second stage crystallization unit was 8.5°C.

[0099] In addition, the first mother liquor stream branched from the solid-liquid separator of the first stage contained acrylic acid (73.7 wt%), acetic acid (6.5 wt%), and water (13.7 wt%). The mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage was 11% with respect to the mass flow rate of the mixed gas. 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 was 1.4:8.6. The mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage with respect to the mass flow rate of the acrylic acid crystals separated from the solid-liquid separator (b) of the second-stage crystallization unit was 70.3%.

[0100] 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 5.5:4.5.

[0101] As a result, the concentrated acrylic acid solution, i.e., purified acrylic acid, obtained by melting the acrylic acid crystals obtained from the solid-liquid separator of the second-stage crystallization unit, contained acrylic acid (99.2 wt%), acetic acid (0.52 wt%), and water (0.18 wt%). In addition, the content of acrylic acid in the upper discharge stream of the absorption tower (acrylic acid loss) was 0.133 mol%.

[0102] Example 3

[0103] In Example 3, the crystallization temperature in the crystallizer of the first stage crystallization unit was -8°C compared to Example 1, and the crystallization temperature in the second stage crystallization unit was 8°C.

[0104] In addition, the first mother liquor stream branched from the solid-liquid separator of the first stage contained acrylic acid (69.6 wt%), acetic acid (7.3 wt%), and water (16.0 wt%). The mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage was 9% with respect to the mass flow rate of the mixed gas. 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 was 1.1:8.9. The mass flow rate of the first mother liquor stream branched from the solid-liquid separator of the first stage with respect to the mass flow rate of the acrylic acid crystals separated in the solid-liquid separator (b) of the second-stage crystallization unit described below was 54.9%.

[0105] 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 was 5.7:4.3.

[0106] As a result, the concentrated acrylic acid solution, i.e., purified acrylic acid, obtained by melting the acrylic acid crystals obtained from the solid-liquid separator of the second-stage crystallization unit, contained acrylic acid (99.2 wt%), acetic acid (0.57 wt%), and water (0.2 wt%). In addition, the content of acrylic acid contained in the upper discharge stream of the absorption tower (acrylic acid loss) was 0.131 mol%.

[0107] Comparative example

[0108] Comparative Example 1

[0109] According to the process diagram shown in Fig. 2, the manufacturing process of acrylic acid was simulated using the Aspen Plus simulator from Aspen.

[0110] 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 absorption tower (100) and the crystallizer (a) of the first stage crystallization unit, respectively.

[0111] Specifically, a mixed gas having the same composition as Example 1 was supplied to an absorption tower (100) and brought into contact with water, an absorption solvent, to obtain an acrylic acid solution. The acrylic acid solution contained acrylic acid (89.3 wt%), acetic acid (3.0 wt%), and water (5.4 wt%).

[0112] The above acrylic acid solution was introduced into 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 3.6°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 first stage crystallization unit was 30 wt%.

[0113] 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.

[0114] 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, and the mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit was supplied to the absorption tower (100). At this time, the mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit contained acrylic acid (87.9 wt%), acetic acid (3.4 wt%), and water (6.2 wt%). The mass flow rate of the mother liquor separated from the solid-liquid separator (b) of the first stage crystallization unit was 762.1% compared to the mass flow rate of the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit described below.

[0115] 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 11.7°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%.

[0116] 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, the solid-liquid separator (b) of the second stage crystallization unit performed solid-liquid separation of the suspension through filtration.

[0117] Meanwhile, 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. The acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit were melted to obtain purified acrylic acid from the concentrated acrylic acid solution.

[0118] As a result, the purified acrylic acid contained acrylic acid (99.6 wt%), acetic acid (0.23 wt%), and water (0.07 wt%). In addition, the content of acrylic acid (acrylic acid loss) contained in the upper discharge stream of the absorption tower was 0.175 mol%.

[0119] In Comparative Example 1, although the flow rate of the mother liquor separated from the solid-liquid separator (b) of the first-stage crystallization unit is high compared to the flow rate of the acrylic acid crystals separated from the solid-liquid separator (b) of the second-stage crystallization unit, the content of acrylic acid contained in the mother liquor separated from the solid-liquid separator (b) of the first-stage crystallization unit is also high, so it was confirmed that the amount of acrylic acid lost through the upper discharge stream of the absorption tower was the highest. In addition, because the flow rate of the mother liquor separated from the solid-liquid separator (b) of the first-stage crystallization unit is high, there may arise a problem that the size of the equipment, for example, the absorption tower, the crystallizer of the first-stage crystallization unit, and the solid-liquid separator must be large.

[0120] Comparative Example 2

[0121] According to the process diagram shown in Fig. 3, the manufacturing process of acrylic acid was simulated using the Aspen Plus simulator from Aspen.

[0122] Specifically, a mixed gas having the same composition as Example 1 was supplied to an absorption tower (100) and brought into contact with water, an absorption solvent, to obtain an acrylic acid solution. The acrylic acid solution contained acrylic acid (88.8 wt%), acetic acid (2.98 wt%), and water (6.2 wt%).

[0123] 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 1.6°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%.

[0124] 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. 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.

[0125] 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 -1.7°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%.

[0126] 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. 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.

[0127] The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was circulated to the absorption tower (100). The mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit contained acrylic acid (79.0 wt%), acetic acid (5.1 wt%), and water (12.0 wt%). The mass flow rate of the mother liquor separated from the solid-liquid separator (b) of the second stage crystallization unit was 92.4% compared to the mass flow rate of the acrylic acid crystals separated from the solid-liquid separator (b) of the second stage crystallization unit.

[0128] Meanwhile, the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the second stage crystallization unit formed a mixed stream with the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the first stage crystallization unit, and the mixed stream was obtained as purified acrylic acid.

[0129] As a result, the purified acrylic acid contained acrylic acid (97.9 wt%), acetic acid (1.0 wt%), and water (0.86 wt%). In addition, the content of acrylic acid (acrylic acid loss) contained in the upper discharge stream of the absorption tower was 0.135 mol%.

[0130] Comparative Example 2 is similar to the Example in the amount of acrylic acid lost through the upper discharge stream of the absorption tower, but it can be confirmed that the purity of the purified acrylic acid, i.e., the content of acrylic acid contained in the purified acrylic acid, is inferior to the Example.

[0131] Meanwhile, in the above-described Examples 1 to 3 of the present invention, a concentrated acrylic acid solution is obtained from a crystallization unit, and the concentrated acrylic acid solution is supplied to a subsequent crystallization unit for further crystallization, but the mother liquor separated from the solid-liquid separator of each stage is not supplied to the subsequent stage. That is, the above-described Examples 1 to 3 present an embodiment in which the concentration of acrylic acid in the acrylic acid solution increases as it goes to the subsequent stage, and ultimately, purified acrylic acid is obtained from the acrylic acid solution discharged from the subsequent crystallization unit.

[0132] On the other hand, Comparative Examples 3 to 5 below are embodiments of the present invention in that they include multiple crystallization units including a crystallizer and a solid-liquid separator, similar to Examples 1 to 3, but they are embodiments of the present invention in which the solid-liquid separated acrylic acid solution is supplied to the crystallizer of the corresponding stage or the crystallizer of the previous stage to obtain purified acrylic acid from the crystallization unit of the first stage, and the solid-liquid separated mother liquor is supplied to the crystallization unit of the subsequent stage to concentrate the mother liquor as it passes through the stages.

[0133] Comparative Example 3

[0134] Comparative Example 3 simulated the manufacturing process of acrylic acid using the Aspen Plus simulator from Aspen, similar to Example 1, according to the process diagram shown in Fig. 4.

[0135] As in Example 1, the side discharge stream of the absorption tower and the top discharge stream of the high-boiling-point by-product removal tower that had undergone the same process as in Example 1 were mixed, and the mixed stream containing acrylic acid (88.8 wt%), acetic acid (2.98 wt%), and water (5.7 wt%) was introduced into a multi-stage crystallization process in which a total of two stages of crystallization units were connected.

[0136] As illustrated in Fig. 4, in Comparative Example 3, the mother liquor separated from the solid-liquid separator of the first stage crystallization unit was supplied to the crystallizer (a) of the second crystallization unit to perform additional crystallization, and the acrylic acid solution separated from the solid-liquid separator (b) of the second crystallization unit was circulated to the crystallizer (a) of the first crystallization unit. Purified acrylic acid was obtained from the concentrated acrylic acid solution obtained by melting the acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit.

[0137] Specifically, as a result of crystallization at a crystallization temperature of -2°C in the crystallizer (a) of the first stage crystallization unit, similar to Example 1, 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 found to be 55 wt%, which was a very high level. As a result, mixing of the suspension was difficult in the crystallizer (a) of the first stage crystallization unit, and thus purified acrylic acid could not be obtained through a subsequent process.

[0138] Comparative Example 4

[0139] Comparative Example 4, similar to Comparative Example 3, carried out an acrylic acid manufacturing process according to the process diagram shown in FIG. 4, but the crystallization temperature of the crystallizer (a) of the first stage crystallization unit was controlled to 3.3°C so that the mass ratio of the acrylic acid crystals contained in the suspension discharged from the crystallizer (a) of the first stage crystallization unit was 30 wt%.

[0140] The suspension discharged from the crystallizer (a) of the first stage crystallization unit was subjected to solid-liquid separation in the solid-liquid separator (b) of the first stage crystallization unit, and the mother liquid was supplied to the crystallizer (a) of the second stage crystallization unit, and purified acrylic acid was obtained from the concentrated acrylic acid solution.

[0141] Additional crystallization of the mother liquor was performed in the crystallizer (a) of the second stage crystallization unit, and the mass ratio of acrylic acid crystals in the discharged suspension was 30 wt%. In order to maintain the mass ratio of acrylic acid crystals in the discharged suspension at 30 wt%, as in Example 1, the crystallization temperature of the crystallizer (a) of the second stage crystallization unit was controlled to 0.7°C.

[0142] The suspension discharged from the crystallizer (a) of the second stage crystallization unit was subjected to solid-liquid separation in the solid-liquid separator (b) of the second stage crystallization unit. The concentrated acrylic acid solution separated in the solid-liquid separator (b) of the second crystallization unit was circulated to the crystallizer (a) of the first crystallization unit, and the separated mother liquor was supplied to the absorption tower (100).

[0143] Meanwhile, purified acrylic acid was obtained from a concentrated acrylic acid solution obtained by melting acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit. As a result, the purified acrylic acid contained acrylic acid (98.5 wt%), acetic acid (0.75 wt%), and water (0.6 wt%).

[0144] The content of acrylic acid (acrylic acid loss) contained in the upper discharge stream of the above absorption tower was 0.144 mol%.

[0145] As a result, it can be confirmed that in Comparative Example 4, not only is the purity (acrylic acid content) of the purified acrylic acid lower than in Example 1, but the amount of acrylic acid lost through the upper discharge stream of the absorption tower also increases.

[0146] Comparative Example 5

[0147] Comparative Example 5 simulated the manufacturing process of acrylic acid using the Aspen Plus simulator from Aspen, similar to Example 1, according to the process diagram shown in Fig. 5.

[0148] Comparative Example 5 produced acrylic acid according to the same process flow as Comparative Example 4, except that a portion of the mother liquor from the solid-liquid separator (b) of the first-stage crystallization unit was branched and supplied to the crystallizer of the first-stage crystallization unit, and the remainder of the mother liquor was supplied to the crystallizer of the second-stage crystallization unit.

[0149] The temperature of the crystallizer (a) of the first stage crystallization unit was set to -2°C as in Example 1, and in order to maintain the mass ratio of acrylic acid crystals in the suspension discharged from each of the crystallizers (a) of the first and second stages at 30 wt% as in Example 1, the flow rate of the mother liquor supplied to the crystallizer (a) of the first stage crystallization unit among the mother liquor of the solid-liquid separator (b) of the first stage crystallization unit was 2.3 times the flow rate of the mother liquor supplied to the crystallizer (a) of the second stage crystallization unit. Meanwhile, purified acrylic acid was obtained from a concentrated acrylic acid solution obtained by melting the acrylic acid crystals separated from the solid-liquid separator (b) of the first stage crystallization unit. As a result, the purified acrylic acid contained acrylic acid (97.5 wt%), acetic acid (1.14 wt%), and water (1.19 wt%).

[0150] The content of acrylic acid (acrylic acid loss) contained in the upper discharge stream of the above absorption tower was 0.132 mol%.

[0151] As a result, it can be seen that in Comparative Example 5, the content of acrylic acid lost to the upper discharge stream of the absorption tower was at the same level as in Example 1, but the content (purity) of acrylic acid in the purified acrylic acid obtained from the solid-liquid separator (b) of the first stage crystallization unit was decreasing.

[0152]

[0153] [Explanation of symbols]

[0154] (a): Crystallizer

[0155] (b): High-liquid separator

[0156] 100: Absorption tower

Claims

1. Contacting a mixed gas containing acrylic acid with water in an absorption tower to obtain an acrylic acid solution containing acrylic acid, The crystallization of the above acrylic acid is performed by a multi-stage crystallization process in which two or more crystallization units including a crystallizer and a solid-liquid separator are connected in series, The above acrylic acid solution is introduced into the crystallizer of the first crystallization unit among the two or more crystallization units, 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 of the stage in which the solid-liquid separator from which the mother liquor is separated or to the absorption tower, 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. A method for producing acrylic acid, wherein purified acrylic acid is obtained from a solid-liquid separator of the last crystallization unit among the above two or more crystallization units.

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 mother liquor obtained from the solid-liquid separator of the first stage crystallization unit is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream divided from the solid-liquid separator of the first stage is circulated to the absorption tower and the second mother liquor stream divided from the solid-liquid separator of the first stage is circulated to the crystallizer of the first stage crystallization unit.

5. In paragraph 4, A method for producing acrylic acid, wherein the position at which the first mother liquor stream branched from the solid-liquid separator of the first stage is circulated to the absorption tower is 10% to 60% downward from the top of the absorption tower, with the top of the absorption tower as 0% as the standard.

6. In paragraph 4, A method for producing acrylic acid, wherein the mass flow rate of the first mother liquid stream branched from the solid-liquid separator of the first stage is 5 to 50% of the mass flow rate of the mixed gas containing the acrylic acid.

7. 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 -9 to 5 ℃, A method for producing acrylic acid, wherein the crystallization temperature in the crystallizer of the second stage crystallization unit is 0 to 12°C.

8. In paragraph 7, 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 1:9 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.

9. In paragraph 1, A method for producing acrylic acid, wherein the mixed gas containing the acrylic acid is a reaction product of a gaseous oxidation reaction of a reactant containing an oxygen-containing gas and a raw material compound.

10. In paragraph 9, 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 acrolein.

11. 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.

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