Method for purifying 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 dated May 10, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] 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. [Background technology]

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

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

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

[0006] The CHDM production process uses water as a solvent, but since the starting material phthalate has low solubility in water, more than 80% of the reaction system remains water after CHDM production. Water is a solvent with a high specific heat, so removing water through a typical separation process is very energy inefficient. In addition, CHDM has a hydroxyl group and is highly hydrophilic to water. Therefore, when removing the solvent from the crude CHDM product to recover CHDM, there is a high risk that the concentration of CHDM associated with water will increase. If the concentration of CHDM associated with water increases, CHDM will be lost, significantly reducing the economic efficiency of the process and also having a negative impact on the environment.

[0007] This necessitates the need for a process for effectively removing the solvent from the crude product obtained after the preparation of the present CHDM. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention is intended to solve the above-mentioned problems, and relates to a method for purifying a 1,4-cyclohexanedimethanol composition having high purity, which can efficiently remove water, which is a solvent for a 1,4-cyclohexanedimethanol crude composition, with low energy consumption and low contents of by-products and water. [Means for solving the problem]

[0009] In order to solve the above problem, one aspect of the present invention is The first step is to feed a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE), evaporate a first stream containing water as a main component in the upper part of the FFE, and separate a second stream containing CHDM as a main component in the lower part; a second step of transferring the first stream to an absorber and recovering CHDM in a lower portion of the absorber; and The third step is to compress the stream discharged from the top of the absorption tower in the second step using an MVR (Mechanical Vapor Compressor) and use it as a heat source for the FFE; The present invention provides a method for purifying a 1,4-cyclohexanedimethanol composition, comprising: Effect of the Invention

[0010] The method for purifying 1,4-cyclohexanedimethanol of the present invention consumes little energy and has a high efficiency in removing water, which is a solvent, so that high-quality 1,4-cyclohexanedimethanol can be produced at low cost.

[0011] In addition, according to the method for purifying a 1,4-cyclohexanedimethanol composition of the present invention, it is possible to provide 1,4-cyclohexanedimethanol with high purity, since the contents of by-products and water are extremely low. This is expected to improve the physical properties when used as a polymer raw material. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a method for purifying a 1,4-cyclohexanedimethanol composition according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a method for purifying a 1,4-cyclohexanedimethanol composition according to a comparative example. [Diagram 3] FIG. 3 is a schematic diagram showing a method for purifying a 1,4-cyclohexanedimethanol composition according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this specification, the terms "include", "comprise", "have" and the like are intended to specify the presence of an implemented feature, step, component, or combination thereof, and should be understood not to preclude the presence or additional possibility of one or more other features, steps, components, or combinations thereof.

[0014] Since the present invention can be modified in various ways and can have various forms, specific embodiments are exemplified and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0015] The method for purifying 1,4-cyclohexanedimethanol of the present invention includes a first step of feeding a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE) and evaporating a first stream containing water as a main component in the upper part of the FFE and separating a second stream containing CHDM as a main component in the lower part; a second step of transferring the first stream to an absorber and recovering CHDM in the lower part of the absorber; and a third step of compressing the stream discharged to the upper part of the absorber in the second step with a Mechanical Vapor Compressor (MVR) and using it as a heat source for the FFE.

[0016] Hereinafter, each step of the method for purifying a 1,4-cyclohexanedimethanol composition according to an embodiment of the present invention will be described in detail with reference to the drawings.

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

[0018] First, a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products is fed into a Falling Film Evaporator (FFE), and the first step is performed in which a first stream containing water as a main component is evaporated at the top of the FFE, and a second stream containing CHDM as a main component is separated at the bottom.

[0019] The 1,4-cyclohexanedimethanol crude composition to be purified by the purification method of the present invention is obtained by, but is not limited to, a second-stage hydrogenation reaction of terephthalic acid. Terephthalic acid, which is an initial reactant, is hydrogenated in a state dissolved in water. However, since terephthalic acid has low solubility in water, the 1,4-cyclohexanedimethanol crude composition contains a large amount of water.

[0020] For example, the 1,4-cyclohexanedimethanol crude composition contains 10 to 40 wt% CHDM, 60 to 90 wt% water, and a small amount of by-products based on the total weight of the composition, with the majority of the remaining components excluding the 10 to 40 wt% CHDM being water.

[0021] However, since water is a solvent with a high specific heat, removing water through a typical separation process is very energy inefficient. In addition, CHDM has a hydroxyl group and is highly hydrophilic to water. Therefore, when removing water from the crude CHDM product to recover CHDM, the concentration of CHDM associated with the water is likely to increase. If the concentration of CHDM associated with the water increases, CHDM is lost, significantly reducing the economic efficiency of the process and also having a negative impact on the environment. Therefore, in order to recover purified CHDM, it is necessary to remove water with low energy and reduce the concentration of CHDM associated with the water as much as possible.

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

[0023] FFE (Falling Film Evaporator) is a type of evaporator that evaporates the target material by making it flow in a thin film from the top of a heating tube. FFE is capable of realizing a continuous evaporation process and has the advantage of being able to remove solvents more efficiently than normal evaporators because it evaporates the solvent through a wide surface area and thin film.

[0024] Referring to FIG. 1, a first step is performed in which a crude 1,4-cyclohexanedimethanol composition 1, which is the target of purification in the present invention, is fed into an FFE 10, a first stream 3 containing water as a main component is evaporated from the upper part of the FFE 10, and a second stream 2 containing CHDM as a main component is separated from the lower part.

[0025] In the present specification, the term "contains as a major component" means that the component is contained in an amount of 60% by weight or more based on the total weight of the stream.

[0026] In the present specification, "barg" means bar gauge pressure, which is the actual pressure at the measurement location minus atmospheric pressure.

[0027] As an example, in the first step, the operation of FFE 10 may be carried out at a temperature of 100 to 130° C. and a pressure of 0.1 to 4 barg. More preferably, it may be carried out 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 aforementioned temperature and pressure conditions are deviated from, the water may not be sufficiently removed overhead from FFE 10, requiring additional water removal in downstream steps, and the energy consumption required for purification may be high.

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

[0029] At the bottom of the FFE 10, most of the water is removed from the 1,4-cyclohexanedimethanol crude composition 1 before it is fed into the FFE 10, and a second stream 2 mainly composed of CHDM is separated. According to one embodiment of the present invention, the second stream 2 may contain 95% by weight or more, preferably 96% by weight or more, and more preferably 98% by weight or more of CHDM based on the total weight of CHDM contained in the initial CHDM crude composition 1. The higher the upper limit of CHDM contained in the second stream 2, the more preferable it is, but in terms of energy efficiency, it may be about 99.9% by weight or less, or about 99.5% by weight or less.

[0030] Next, the first stream 3 separated at the upper part of the FFE 10 is transferred to an absorber 20, and a second step of recovering CHDM at the lower part of the absorber is performed.

[0031] In the first step, most of the water is separated from the CHDM crude composition using FFE 10 into the first stream 3, so that most of the water contained in the initial CHDM crude composition 1 is separated into the first stream 3 and a second stream 2 of purified CHDM can be separated at the bottom. However, the first stream 3 separated at the top still contains about 1 wt. % CHDM based on the total weight of CHDM contained in the initial CHDM crude composition 1.

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

[0033] That is, the second step is a step of distilling the first stream 3, which has been subjected to the separation step of the first step using the FFE 10, in the absorption tower 20 to separate by-products and water at the top and separate and recover CHDM at the bottom.

[0034] In this case, cooling water at 20 to 50° C., preferably 25 to 35° C., may be fed to the absorption tower 20 in the second step, and the amount of recovered CHDM may increase depending on the amount of cooling water fed. Meanwhile, since the recovered CHDM stream 4 is combined with the second stream 2 separated at the bottom of the FFE 10 in the first step and is included in the CHDM concentrated stream 7, the more the amount of cooling water used, the more energy is required during treatment in the subsequent steps, which reduces the economic efficiency, so it is necessary to use an appropriate amount of cooling water.

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

[0036] According to one embodiment of the present invention, by the second step as described above, 50 wt % or more, preferably 55 wt % or more, and more preferably 60 wt % or more of the CHDM contained in first stream 3 input to absorption tower 20 can be recovered as CHDM stream 4. The higher the upper limit of CHDM recovered as CHDM stream 4, the more preferable, but from the viewpoint of energy efficiency, it may be about 90 wt % or less, or about 80 wt % or less.

[0037] The recovered CHDM stream 4 is combined with the second stream 2 separated at the bottom of the FFE 10 in the first step and sent to a CHDM concentrated stream 7, which then undergoes downstream processes such as distillation to obtain CHDM with a purity of 99.8% or more.

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

[0039] The third stream 5 discharged to the top of the absorber 20 contains mostly water in a gas phase (about 99% by weight or more) and small amounts of CHDM and by-products.

[0040] If this is compressed using MVR 30 and then circulated through FFE 10 to be used as heat source 6 for FFE 10, the amount of steam consumed in FFE 10 can be reduced, resulting in significant savings in energy consumption.

[0041] The CHDM composition obtained by the purification method of the present invention as 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, in the purified CHDM composition, the CHDM content, i.e., purity, can be 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] Additionally, the purified CHDM composition may have a very low residual water content, such as 0.15 wt. % or less, or 0.13 wt. % or less, or 0.12 wt. % or less, or 0.10 wt. % or less, or 0.09 wt. % or less, or 0.08 wt. % or less, or 0.07 wt. % or less, based on 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 therefore can be usefully used as a raw material for producing high-quality products such as pharmaceuticals, synthetic resins, synthetic fibers, and dyes.

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

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

[0047] The 1,4-cyclohexanedimethanol crude composition, which is the reaction product obtained after the second-stage reaction, contains 1,4-cyclohexanedimethanol containing cis- and trans-isomers, water as a solvent, and reaction by-products. By purifying this crude composition by the purification method of the present application, high-purity 1,4-cyclohexanedimethanol can be obtained.

[0048] The present invention will be described in more detail below for the understanding of the present invention. 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 was provided containing a gas-induced type agitator. The reactor was charged with 3,200 kg of terephthalic acid (TPA) (5 wt%) as a reactant, 16,000 kg of distilled water as a solvent, and 15 wt% of hydrogenation catalyst Pd / C (containing 5 wt% Pd relative to the carrier carbon) based on the total solution including the reactants and the solvent, and the atmosphere inside the reactor was replaced with nitrogen, and 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., the temperature was maintained and the mixture was stirred for 30 minutes to dissolve the TPA. Then, the stirring speed was increased to 100 barg inside the reactor and 300 to 500 m of hydrogen gas per unit volume. 2 / m 3 Hydrogen gas was supplied into the reaction solution so as to maintain the temperature, and the hydrogenation reaction was carried out for 3 hours. After the reaction was completed, a product containing 3,144 kg of 1,4-cyclohexanedimethanol (CHDA) (trans-CHDA ratio of CHDA: 68 wt%) and 16,031 kg of water was obtained. After removing only the hydrogenation catalyst with a metal filter, the product was used as it was as a reactant for the second hydrogenation reaction step.

[0050] Second Phase A second reactor was provided containing a gas-induced type agitator. In the second reactor, 3,144 kg of CHDA (trans-CHDA ratio in CHDA: 68 wt%), 16,031 kg of distilled water as a solvent, and 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) were added at about 57 wt% of the total solution including reactants and solvent, and purged twice with 5 bar of nitrogen and twice with 5 bar of hydrogen, and then the temperature was raised to 230°C while stirring at low speed in a hydrogen atmosphere (about 14 to 15 bar). When the reaction temperature is reached, hydrogen is injected up to the reaction pressure of 100 barg, and the stirring speed is increased until the surface area per unit volume of the hydrogen gas bubbles is 300 to 450 m. 2 / m 3 The reaction was carried out for 6 hours while maintaining the above temperature. The hydrogenation catalyst was removed from the product of the second stage reaction using a metal filter, and then the product was transferred to the purification stage of the embodiment.

[0051] Comparative Example 1 A 1,4-cyclohexanedimethanol composition was purified according to the schematic diagram shown in FIG. First, CHDM crude composition 1a of Production Example 1 was fed into FFE10. Water was removed from upper stream 3a of FFE10, and CHDM was separated into lower stream 2a. When FFE10 was operated so that about 10% water was present in lower stream 2a, the required heat amount was about 5 Gcal / hr, and LPS (low pressure steam) was used as the heat source. At this time, about 20 kg / hr of CHDM was accompanied by upper stream 3a of FFE10. 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 of each stream are shown in Table 1 below. [Table 1]

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

[0054] The top stream 3b was sent to the MVR 30 and was reused as the heat source 4b of the FFE 10 through gas phase compression. The heat value obtained by using the MVR 30 was about 5.3 Gcal / hr, and it was possible to operate without inputting additional heat, and the electricity required for this was about 730 kW, which is equivalent to 0.63 Gcal / hr. Therefore, even taking into account the amount of electricity used, the introduction of the MVR 30 was able to significantly reduce energy use compared to Comparative Example 1. However, there was still a considerable amount (35.8 kg / hr) of unrecovered CHDM in the top stream 3b, and there was no advantage in terms of the recovery rate of CHDM.

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

[0056] Example 1 A 1,4-cyclohexanedimethanol composition was purified according to the schematic diagram shown in FIG. CHDM crude composition 1 of Preparation Example 1 was fed into FFE 10. Water was removed into first stream 3 at the top of FFE 10, and CHDM was separated into second stream 2 at the bottom. When FFE 10 was operated so that about 10% water was present in second stream 2, the required heat was about 5 Gcal / hr, and LPS (low pressure steam) was used as the initial heat source. At this time, first stream 3 also contained about 20 kg / hr of CHDM. Next, the first stream 3 separated at the top of the FFE 10 was transferred to an absorber 20. Cooling water at 30° C. was fed to the absorber 20 at a rate of about 150 kg / hr. The third stream 5 discharged from the top of the absorption tower 20 was compressed in the MVR 30 and reused as a heat source 6 for the FFE, and was recovered as a CHDM stream 4 at the bottom.

[0057] The upper stream 3b in Comparative Example 2 contained about 20 kg / hr of CHDM, whereas the third stream 5 fed to the MVR 30 contained about 8 kg / hr of CHDM, and it was confirmed that about 12 kg / hr of CHDM was re-recovered as the lower CHDM stream 4.

[0058] The calorific value obtained by using the MVR30 is about 5.3 Gcal / hr, and operation is possible without inputting additional calorific value. The electricity required for this is about 730 kW, which is equivalent to 0.63 Gcal / hr. Therefore, even taking into account the amount of electricity used, the introduction of the MVR30 has enabled a significant reduction in energy consumption compared to Comparative Example 1.

[0059] In addition, the organic matter content in the wastewater treated stream was 4454 ppm, which was reduced from the organic matter content of 5717 ppm 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 can efficiently remove water with low energy by using the FFE, the absorption tower, and the MVR, and can separate high-purity CHDM and reduce the organic matter content in the wastewater. [Explanation of symbols]

[0062] 1:1,4-Cyclohexanedimethanol Crude Composition 2: Second stream 3: First stream 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. A first step of feeding a crude CHDM composition containing 1,4-cyclohexanedimethanol (CHDM), water, and by-products into a Falling Film Evaporator (FFE), evaporating a first stream containing water as a main component at the top of the FFE, and separating a second stream containing CHDM as a main component at the bottom; a second step of transferring the first stream to an absorber and recovering CHDM in a lower portion of the absorber; and A third step in which 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; A method for purifying a 1,4-cyclohexanedimethanol composition comprising:

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 wt. % CHDM, 60 to 90 wt. % water, and by-products, based on the total weight of the composition. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

4. The first step separates at least 90 wt. % of water into the first stream, based on the total weight of water contained in the initial CHDM crude composition; A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

5. The first step separates at least 95 wt. % of the CHDM contained in the initial CHDM crude composition into the second stream, based on the total weight of the CHDM contained in the initial CHDM crude composition. A method for purifying the 1,4-cyclohexanedimethanol composition according to claim 1.

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

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

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

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

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

Images