Method for purifying a 1,4-cyclohexanedimethanol composition

Abstract

The present invention relates to a method for purifying a 1,4-cyclohexanedimethanol (CHDM) composition, and more particularly to a method for purifying CHDM that can efficiently remove water, which is a solvent, with low energy and separate high-purity CHDM.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2022 - 0057068 filed on May 10, 2022, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a method for purifying a 1,4 - cyclohexanedimethanol (CHDM) composition. More specifically, it relates to a method for purifying CHDM that can efficiently remove water as a solvent with low energy and separate high - purity CHDM.

Background Art

[0003] 1,4 - Cyclohexanedimethanol (CHDM) is widely used as a raw material for pharmaceuticals, synthetic resins, synthetic fibers, or dyes, and is particularly used as a raw material for polyethylene terephthalate, a polyester friendly to the environment.

[0004] 1,4 - Cyclohexanedimethanol exists as stereoisomers in cis and trans forms, but for higher - quality products, a higher ratio of trans 1,4 - cyclohexanedimethanol (trans CHDM) than cis is required.

[0005] Among the methods for producing 1,4 - cyclohexanedimethanol, there is a method in which phthalate is first hydrogenated to convert it to 1,4 - cyclohexane dicarboxylic acid (CHDA), and then CHDA is hydrogenated to convert it to CHDM. This method consists of a second - stage hydrogenation reaction using a heterogeneous catalyst.

[0006] In this type of CHDM production process, water is used as the solvent, but because the starting material, phthalate, has low solubility in water, water accounts for approximately 80% or more of the reaction system after CHDM production. Since water is a solvent with a high specific heat, removing water through general separation processes is highly energy-inefficient. Furthermore, because CHDM has hydroxyl groups, it exhibits high hydrophilicity towards water. Therefore, when the solvent is removed from the crude CHDM product to recover the CHDM, there is a high risk of an increase in the concentration of CHDM due to the water. If the concentration of CHDM due to water increases, not only will CHDM be lost and the economic efficiency of the process be greatly reduced, but it will also have a negative impact on the environment.

[0007] This necessitates a process for effectively removing the solvent from the crude product obtained after the production of CHDM. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the aforementioned problems and relates to a method for purifying a 1,4-cyclohexanedimethanol crude composition in which water, the solvent, can be efficiently removed with low energy, resulting in a high-purity 1,4-cyclohexanedimethanol composition with low by-product and water content. [Means for solving the problem]

[0009] To solve the aforementioned problems, one aspect of the present invention is: The first step involves placing a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE), evaporating a first stream mainly containing water from the top of the FFE, and separating a second stream mainly containing CHDM from the bottom; A second step involves transferring the first stream to an absorber and recovering CHDM at the bottom of the absorber; and In the third step, the stream discharged from the top of the absorption tower in the second step is compressed by an MVR (Mechanical Vapor Compressor) and used as a heat source for the FFE; The present invention provides a method for purifying a 1,4-cyclohexanedimethanol composition containing [a specific compound / component]. [Effects of the Invention]

[0010] The present invention provides a method for purifying 1,4-cyclohexanedimethanol that consumes little energy and has high efficiency in removing the solvent, water, thus enabling the production of high-quality 1,4-cyclohexanedimethanol at low cost.

[0011] Furthermore, according to the purification method for the 1,4-cyclohexanedimethanol composition of the present invention, the by-product and water content is very low, making it possible to provide 1,4-cyclohexanedimethanol with high purity, and improved physical properties can be expected when used as a polymer raw material. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing a method for purifying a 1,4-cyclohexanedimethanol composition according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing a purification method for a 1,4-cyclohexanedimethanol composition according to a comparative example. [Figure 3] Figure 3 is a schematic diagram showing a purification method for a 1,4-cyclohexanedimethanol composition according to a comparative example. [Modes for carrying out the invention]

[0013] The terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of implemented features, steps, components, or combinations thereof, and should not be understood to presuppose the existence or possibility of adding one or more other features, steps, components, or combinations thereof.

[0014] Because the present invention can be modified in various ways and take many forms, specific embodiments are illustrated and described in detail below. However, this should not be understood as limiting the present invention to the specific disclosure, but rather as including all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0015] The present invention provides a method for purifying 1,4-cyclohexanedimethanol, comprising: a first step of introducing a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE), evaporating a first stream mainly containing water at the top of the FFE, and separating a second stream mainly containing CHDM at the bottom; a second step of transferring the first stream to an absorber and recovering CHDM at the bottom of the absorber; and a third step of compressing the stream discharged at the top of the absorber in the second step using a Mechanical Vapor Compressor (MVR) and using it as a heat source for the FFE.

[0016] The following describes in detail, step by step, a method for purifying a 1,4-cyclohexanedimethanol composition according to one embodiment of the present invention, with reference to the drawings.

[0017] FIG. 1 is a schematic diagram showing a method for purifying a 1,4 - cyclohexanedimethanol composition according to an embodiment of the present invention.

[0018] First, a crude CHDM composition containing 1,4 - cyclohexanedimethanol (1,4 - CHDM), water, and by - products is fed into a Falling Film Evaporator (FFE). A first step is performed to evaporate a first stream containing water as a main component at the upper part of the FFE and separate a second stream containing 1,4 - CHDM as a main component at the lower part.

[0019] The crude 1,4 - cyclohexanedimethanol composition to be purified by the purification method of the present invention is, but not limited to, obtained by a second - stage hydrogenation reaction with respect to terephthalic acid. The first reactant, terephthalic acid, undergoes a hydrogenation reaction in a state dissolved in water. However, due to its low solubility in water, the crude 1,4 - cyclohexanedimethanol composition contains a large amount of water.

[0020] As an example, the crude 1,4 - cyclohexanedimethanol composition contains 10 to 40% by weight of CHDM, 60 to 90% by weight of water, and a small amount of by - products with respect to the total weight. A substantial portion of the remaining components excluding the 10 to 40% by weight of CHDM is occupied by water.

[0021] By the way, since water is a solvent with a high specific heat, removing water through a general separation process is very energy-inefficient. Also, since CHDM has a hydroxy group, it shows high hydrophilicity to water. However, when removing water from the crude product of CHDM to recover CHDM, there is a great risk that the concentration of CHDM associated with water will increase. If the concentration of CHDM associated with water increases, not only will there be a loss of CHDM, significantly reducing the economic efficiency of the process, but it will also have an adverse impact on the environment. Therefore, it is necessary to remove water with low energy to recover purified CHDM and reduce the concentration of CHDM associated with water as much as possible.

[0022] Thus, in one embodiment of the present invention, first, a step of removing water from the CHDM crude composition using a Falling Film Evaporator (FFE) is performed.

[0023] The Falling Film Evaporator (FFE) is a type of evaporator that evaporates the object by flowing it in a thin film form from the upper part of the heating tube. The FFE can realize a continuous evaporation process and evaporate the solvent through a wide surface area and a thin film, so it has the advantage of being able to remove the solvent with higher efficiency than ordinary evaporators.

[0024] Referring to FIG. 1, a first step is performed in which the 1,4-cyclohexanedimethanol crude composition 1, which is the object to be purified in the present invention, is introduced into the FFE 10, the first stream 3 mainly containing water is evaporated at the upper part of the FFE 10, and the second stream 2 mainly containing CHDM is separated at the lower part.

[0025] In the specification of the present invention, "containing as the main component" means containing the component at 60% by weight or more in the total weight of the stream.

[0026] In the specification of the present invention, "barg" means gauge pressure, which is the pressure obtained by subtracting atmospheric pressure from the actual pressure at the measurement position.

[0027] For example, in the first step, the FFE10 may be operated at a temperature of 100 to 130°C and a pressure of 0.1 to 4 barg. More preferably, it may be operated at a temperature of 115 to 125°C and a pressure of 0.5 to 3 barg, or at a temperature of 118 to 123°C and a pressure of 0.5 to 2 barg. If the temperature and pressure conditions deviate from those described above, water may not be sufficiently removed from the top of the FFE10, requiring additional water removal in subsequent steps, which may increase the energy consumption required for purification.

[0028] Through the first step described above, 90% by weight or more, preferably 92% by weight or more, and more preferably 95% by weight or more of the total weight of water contained in the initial CHDM crude composition 1, can be evaporated to the top of the FFE 10 and separated into the first stream 3. The upper limit of water contained in the first stream 3 is preferable as it is higher, but for energy efficiency reasons it may be about 99% by weight or less, or about 98% by weight or less.

[0029] At the bottom of FFE10, a second stream 2 is separated, in which most of the water has been removed from the 1,4-cyclohexanedimethanol crude composition 1 before it was introduced into FFE10, and CHDM is the main component. According to one embodiment of the present invention, the second stream 2 may contain 95% or more by weight of CHDM, preferably 96% or more by weight, and more preferably 98% or more by weight, relative to the total weight of CHDM contained in the initial CHDM crude composition 1. The upper limit of CHDM contained in the second stream 2 is preferable as it is higher, but for energy efficiency reasons, it may be about 99.9% or less by weight, or about 99.5% or less by weight.

[0030] Next, a second step is performed in which the first stream 3 separated at the top of the FFE 10 is transferred to the absorber 20, and the CHDM is recovered at the bottom of the absorber.

[0031] In the first step, by separating most of the water from the CHDM crude composition into the first stream 3 using FFE 10, a large amount of water contained in the initial CHDM crude composition 1 is separated into the first stream 3, and a second stream 2 of purified CHDM may be separated at the bottom, but the first stream 3 separated at the top still contains about 1% by weight of CHDM relative to the total weight of CHDM contained in the initial CHDM crude composition 1.

[0032] In the second step described above, such excess CHDM contained in the first stream 3 is recovered in the absorption tower 20.

[0033] In other words, the second step involves the first stream 3, which has gone through the separation step of the first step using FFE10, being absorbed by the absorption tower 20. Absorbed by contact with cooling water Top teeth This step involves separating the by-products from the water and then separating and recovering the CHDM at the bottom.

[0034] At this time, cooling water at 20 to 50°C, preferably 25 to 35°C, may be introduced into the absorption tower 20 in the second step, and the amount of CHDM recovered may increase depending on the amount of cooling water introduced. On the other hand, the recovered CHDM stream 4 merges with the second stream 2 separated at the bottom of the FFE 10 in the first step and is included in the CHDM enrichment stream 7, so the more cooling water used, the more energy is required for processing in the subsequent steps, and the less economical it becomes, so it is necessary to use an appropriate amount.

[0035] Therefore, according to one embodiment of the present invention, when the amount of CHDM contained in the first stream 3 fed into the absorption tower 20 is about 15 to 25 kg / hr, it is preferable from the viewpoint of both CHDM recovery rate and economic efficiency to feed cooling water into the absorption tower 20 at a rate of about 100 to 200 kg / hr, preferably about 120 to 180 kg / hr.

[0036] According to one embodiment of the present invention, by the second step described above, 50% or more by weight, preferably 55% or more by weight, and more preferably 60% or more of CHDM can be recovered as CHDM stream 4, relative to the total weight of CHDM contained in the first stream 3 fed into the absorption tower 20. While a higher upper limit is preferable for the CHDM recovered as CHDM stream 4, for energy efficiency reasons, it may be about 90% or less by weight, or about 80% or less by weight.

[0037] The recovered CHDM stream 4 merges with the second stream 2, which is separated at the bottom of the FFE 10 in the first step, and is sent to the CHDM concentration stream 7, where it is subsequently obtained as CHDM with a purity of 99.8% or higher through a subsequent process such as distillation.

[0038] Next, a third step is performed in which the third stream 5 discharged to the top of the absorption tower 20 in the second step is compressed with an MVR (Mechanical Vapor Compressor) and used as a heat source 6 for the FFE.

[0039] The third stream 5 discharged from the top of the absorption tower 20 consists mostly of water in the gas phase (approximately 99% by weight or more), with small amounts of CHDM and by-products.

[0040] By compressing this using the MVR30 and then circulating it through the FFE10 to use as the heat source 6 for the FFE10, the amount of steam consumed by the FFE10 can be reduced, resulting in significant energy savings.

[0041] The CHDM composition obtained by the purification method of the present invention described above may have a CHDM purity of 99.5% by weight or more, calculated as the CHDM content measured by gas chromatography (GC) analysis.

[0042] More specifically, the purified CHDM composition may have a CHDM content, i.e., purity of 99.5% by weight or more, or 99.7% by weight or more, or 99.75% by weight or more, or 99.8% by weight or more.

[0043] Furthermore, the water content remaining in the purified CHDM composition can be very low, being 0.15% by weight or less, or 0.13% by weight or less, or 0.12% by weight or less, or 0.10% by weight or less, or 0.09% by weight or less, or 0.08% by weight or less, or 0.07% by weight or less, relative to the total weight of the purified CHDM composition.

[0044] As described above, the CHDM obtained by the purification method of the present invention has high purity and very low content of residual water and by-products, and can therefore be usefully used as a raw material for producing high-quality products such as pharmaceuticals, synthetic resins, synthetic fibers, or dyes.

[0045] The 1,4-cyclohexanedimethanol crude composition targeted by the purification method of the present invention described above may be produced by a first-step hydrogenation reaction to 1,4-cyclohexanedicarboxylic acid (CHDA) using terephthalic acid as a starting material, and a second-step hydrogenation reaction from 1,4-cyclohexanedicarboxylic acid to 1,4-cyclohexanedimethanol.

[0046] For example, the product may be produced by a production method comprising: a first step of supplying a reaction solution containing terephthalic acid, a first hydrogenation catalyst, and water, and hydrogen gas to a first reactor equipped with a stirrer to carry out a hydrogenation reaction to produce 1,4-cyclohexanedicarboxylic acid (CHDA) containing cis and trans isomers; and a second step of supplying a reaction solution containing the reaction product from the first step, a second hydrogenation catalyst, and water, and hydrogen gas to a second reactor equipped with a stirrer to carry out a hydrogenation reaction to produce 1,4-cyclohexanedimethanol (CHDM) containing cis and trans isomers, but the present invention is not limited thereto.

[0047] The crude 1,4-cyclohexanedimethanol composition obtained after the second step of the reaction contains 1,4-cyclohexanedimethanol including cis and trans isomers, water as a solvent, and reaction by-products. This can be purified by the purification method of the present invention to obtain high-purity 1,4-cyclohexanedimethanol.

[0048] The present invention will be described in more detail below for better understanding. However, the following examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples. [Examples]

[0049] Manufacturing Example 1 Phase 1 A first reactor, including a gas-induced stirrer, was prepared. 3,200 kg of terephthalic acid (TPA), 5% by weight, 16,000 kg of distilled water, the solvent, and 15% by mass of the hydrogenation catalyst Pd / C (containing 5% by weight of Pd relative to the support carbon) were added to the reactor. After replacing the air inside the reactor with nitrogen, the temperature of the mixed solution was raised to 170°C while stirring at a low speed. After the temperature of the mixed solution reached 170°C, it was stirred for 30 minutes while maintaining the temperature to dissolve the TPA. After this, the stirring speed was increased until the reactor interior reached 100 barg and the surface area per unit volume of hydrogen gas reached 300 to 500 m³. 2 / m 3 The hydrogenation reaction was carried out for 3 hours while supplying hydrogen gas into the reaction solution to maintain the desired level. After the reaction was complete, a product was obtained containing 3,144 kg of 1,4-cyclohexanedimethanol (CHDA) (trans-CHDA ratio: 68 wt%) and 16,031 kg of water. After removing only the hydrogenation catalyst using a metal filter, the product was used directly as the reactant in the second hydrogenation reaction step.

[0050] Phase 2 A second reactor, including a gas-induced stirrer, was prepared. In the second reactor, 3,144 kg of CHDA (of which trans-CHDA ratio: 68% by weight), which is the product of the first-stage reaction, and 16,031 kg of distilled water, which is the solvent, were added, along with a catalyst (ruthenium-tin / carbon catalyst, containing 5 parts by weight of ruthenium and 5.8 parts by weight of tin per 100 parts by weight of carbon support) at a concentration of approximately 57% by mass relative to the total solution containing the reactants and solvent. After purging twice with nitrogen at 5 bar and twice with hydrogen at 5 bar, the temperature was raised to 230°C while stirring at low speed in a hydrogen atmosphere (approximately 14-15 bar). Once the reaction temperature is reached, hydrogen is injected up to the reaction pressure of 100 barg, and then the stirring speed is increased until the surface area per unit volume of hydrogen gas bubbles reaches 300 to 450 m³. 2 / m 3 The reaction was carried out for 6 hours while maintaining the desired conditions. After removing the hydrogenation catalyst from the product of the second step reaction using a metal filter, the product was transferred to the purification step of the example.

[0051] Comparative Example 1 The 1,4-cyclohexanedimethanol composition was purified according to the schematic diagram shown in Figure 2. First, the crude CHDM composition 1a from Production Example 1 was added to FFE10. Water was removed from the upper stream 3a of FFE10, and CHDM was separated into the lower stream 2a. When FFE10 was operated so that approximately 10% water was present in the lower stream 2a, the required heat was approximately 5 Gcal / hr, and LPS (Low-pressure steam) was used as the heat source. At this time, the upper stream 3a of FFE10 contained approximately 20 kg / hr of CHDM. The upper stream 3a was then treated as wastewater, and the organic matter content in the upper stream 3a was 5717 ppm.

[0052] The temperature, pressure, and composition for each stream are shown in Table 1 below. [Table 1]

[0053] Comparative Example 2 The 1,4-cyclohexanedimethanol composition was purified according to the schematic diagram shown in Figure 3. First, the crude CHDM composition 1b from Production Example 1 was added to FFE10. Water was removed from the upper stream 3b of FFE10, and CHDM was separated into the lower stream 2b. When FFE10 was operated so that approximately 10% water was present in the lower stream 2b, the required heat was approximately 5 Gcal / hr, and LPS (Low-pressure steam) was used as the initial heat source. At this time, approximately 20 kg / hr of CHDM was also present in the upper stream 3b.

[0054] The upper stream 3b was sent to the MVR30 and reused as the heat source 4b for the FFE10 through gas-phase compression. The amount of heat obtained using the MVR30 was approximately 5.3 Gcal / hr, and operation was possible without additional heat input. The electricity required at this time was approximately 730 kW, which is equivalent to 0.63 Gcal / hr. Therefore, even considering the electricity consumption, the introduction of the MVR30 resulted in a significant reduction in energy consumption compared to Comparative Example 1. However, a considerable amount of CHDM (35.8 kg / hr) still remained unrecovered due to the upper stream 3b, and from the perspective of CHDM recovery rate, there was no advantage.

[0055] The temperature, pressure, and composition for each stream are shown in Table 2 below. [Table 2]

[0056] Example 1 The 1,4-cyclohexanedimethanol composition was purified according to the schematic diagram shown in Figure 1. Crude CHDM composition 1 from Production Example 1 was added to FFE10. Water was removed from the upper first stream 3 of FFE10, and CHDM was separated into the lower second stream 2. When FFE10 was operated so that approximately 10% water was present in the second stream 2, the required heat was approximately 5 Gcal / hr, and LPS (Low-pressure steam) was used as the initial heat source. At this time, approximately 20 kg / hr of CHDM was also present in the first stream 3. Next, the first stream 3 separated at the top of the FFE 10 was transferred to the absorber 20. Cooling water at 30°C was supplied to the absorber 20 at a rate of approximately 150 kg / hr. The third stream 5, discharged to the top of the absorption tower 20, is compressed in the MVR 30 and reused as the heat source 6 for the FFE, while the lower part is recovered as the CHDM stream 4.

[0057] In Comparative Example 2, the upper stream 3b contained approximately 20 kg / hr of CHDM, while the third stream 5 fed to the MVR 30 contained approximately 8 kg / hr of CHDM, confirming that approximately 12 kg / hr of CHDM was recovered as the lower CHDM stream 4.

[0058] The amount of heat obtained using the MVR30 is approximately 5.3 Gcal / hr, and it can be operated without any additional heat input. The electricity required at this time is approximately 730 kW, which is equivalent to 0.63 Gcal / hr. Therefore, even considering the amount of electricity used, the introduction of the MVR30 resulted in a significant reduction in energy consumption compared to Comparative Example 1.

[0059] Furthermore, the organic matter content in the wastewater treatment stream was 4454 ppm, which is lower than the 5717 ppm organic matter content in Comparative Example 1.

[0060] The temperature, pressure, and composition for each stream are shown in Table 3 below. [Table 3]

[0061] As described above, it was confirmed that the purification method according to the embodiment of the present invention, by using FFE, absorption tower, and MVR, can efficiently remove water with low energy, separate high-purity CHDM, and reduce the organic matter content in wastewater. [Explanation of symbols]

[0062] 1:1,4-Cyclohexanedimethanol crude composition 2: Second Stream 3: Stream 1 4: CHDM stream 5: Third Stream 6:Heat source 7: CHDM concentrated stream 10:FFE(Falling Film Evaporator) 20: Absorber 30:MVR(Mechanical Vapor Compressor)

Claims

1. The first step involves placing a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE), evaporating a first stream mainly containing water from the top of the FFE, and separating a second stream mainly containing CHDM from the bottom; A second step involves transferring the first stream to an absorber and recovering CHDM at the bottom of the absorber; and In the third step, the stream discharged to the top of the absorption tower in the second step is compressed with an MVR (Mechanical Vapor Compressor) and used as a heat source for the FFE; A method for purifying a 1,4-cyclohexanedimethanol composition containing [the specified substance].

2. The FFE is operated at a temperature of 100 to 130°C and a pressure of 0.1 to 4 barg. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

3. The CHDM crude composition comprises 10 to 40% by weight of CHDM, 60 to 90% by weight of water, and by-products, A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

4. In the first step, at least 90% by weight of water, relative to the total weight of water contained in the initial crude CHDM composition, is separated into the first stream. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

5. The method for purifying a 1,4-cyclohexanedimethanol composition according to claim 1, wherein the first step separates 95% by weight or more of CHDM, relative to the total weight of CHDM contained in the initial crude CHDM composition, into the second stream.

6. Cooling water at 20 to 50°C is introduced into the absorption tower. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

7. The CHDM contained in the first stream fed into the absorption tower is 15 to 25 kg / hr, and 100 to 200 kg / hr of cooling water is fed into the absorption tower. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 6.

8. In the second step, 50% by weight or more of the CHDM contained in the first stream fed into the absorption tower is recovered as a CHDM stream. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

9. The method for purifying a 1,4-cyclohexanedimethanol composition according to claim 8, wherein the recovered CHDM stream is merged with the second stream separated at the bottom of the FFE in the first step and sent to a CHDM enrichment stream.

10. The aforementioned CHDM crude composition, It is produced by a first-step hydrogenation reaction using terephthalic acid as a starting material to 1,4-cyclohexanedicarboxylic acid (CHDA), and a second-step hydrogenation reaction from 1,4-cyclohexanedicarboxylic acid to 1,4-cyclohexanedimethanol. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

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