A method for purifying high trans-1,4-cyclohexanedimethanol in terephthalate hydrogenation reaction liquid by extractive distillation

Abstract

The application discloses a kind of high trans-1,4-cyclohexanedimethanol in terephthalate ester hydrogenation reaction liquid extraction rectification purification method, belong to product purification technical field.This method with cis-trans 1,4-cyclohexanedimethanol (CHDM) hydrogenation reaction liquid as raw material, after filtration, molecular sieve dehydration obtains pretreated raw material liquid, with imidazole ionic liquid as extractant, raw material liquid and extractant are respectively continuously sent into the middle and upper part of extraction rectification tower, cis CHDM high content light component is obtained at tower top, trans CHDM and the mixture of extractant are obtained at tower bottom;Tower bottom mixture is distilled by solvent recovery tower, and high-purity CHDM product with trans ratio ≥85% is separated out, and the recovered imidazole ionic liquid is recycled after dehydration.The selectivity of the imidazole ionic liquid selected by the application to CHDM cis-trans isomers is excellent, which greatly improves the separation efficiency, the product trans ratio far exceeds the existing industry index, and the extractant can be recycled, the energy consumption is reduced by 30%-50%, the process is easy to control in industrialization, realizes the large-scale efficient purification of CHDM, breaks the foreign technology monopoly, and meets the demand of high-end polyester industry.

Description

Technical Field

[0001] This invention belongs to the field of product purification technology, specifically relating to a method for purifying a CHDM mixture in a terephthalic acid ester hydrogenation reaction solution using an extractive distillation process with imidazole ionic liquid as the extractant, thereby achieving efficient separation of cis-trans isomers and obtaining a high trans ratio CHDM product. Background Technology

[0002] 1,4-Cyclohexanediethanol (CHDM) is a key monomer for the production of high-end polyesters (such as PETG and PCTG). It has two isomers, cis and trans. Polyesters modified with trans CHDM have higher melting points and outstanding application value in high-end fields. A high trans ratio is a core indicator in the industry.

[0003] Currently, CHDM is mainly prepared by hydrogenation reduction of dimethyl terephthalate. Due to process limitations, the cis and trans isomers are difficult to separate after the reaction, resulting in a generally low trans ratio in the product. Only a few foreign companies worldwide have the capacity for mass production, and their industry standard trans ratio is only ≥68%. Furthermore, existing purification technologies (crystallization, ordinary distillation, etc.) suffer from low separation efficiency, high energy consumption, and inability to scale up, leading to domestic market reliance on imports and difficulty in meeting the demand for high-end polyester.

[0004] Existing separation methods each have their limitations: crystallization is complex and time-consuming, making it impossible to scale up; ordinary distillation is difficult to separate due to the similar properties of cis and trans isomers and is energy-intensive; gas chromatography is only suitable for small-scale separation in the laboratory and cannot be applied industrially.

[0005] Imidazole ionic liquids, as green solvents, have advantages such as high selectivity and recyclability, and show promising prospects in isomer separation. However, there are currently no reports on their use in CHDM cis-trans isomer extraction, distillation and purification to achieve products with a high trans ratio of over 85%. Summary of the Invention

[0006] Purpose of the invention:

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies in the purification of CHDM, such as low separation efficiency of cis-trans isomers, difficulty in increasing the trans ratio of the product (current foreign industry standards are only ≥68%), high energy consumption, serious solvent pollution, and inability to achieve large-scale industrial production. This invention provides an extractive distillation method for purifying high trans-1,4-cyclohexanediethanol after the reaction. It uses imidazole ionic liquids as extractants to achieve efficient separation of cis-trans isomers, obtaining CHDM products with a trans ratio of over 85%, meeting the application needs of the high-end polyester industry, breaking the foreign technology monopoly, and reducing the domestic market's dependence on imported products. Technical solution:

[0008] I. A method for extractive distillation purification of high trans-1,4-cyclohexanediethanol from a terephthalic acid ester hydrogenation reaction solution, characterized in that a mixture containing cis-1,4-cyclohexanediethanol and trans-1,4-cyclohexanediethanol after the reaction is used as raw material, and an imidazole ionic liquid is used as the extractant. The cis-trans isomers are separated by extractive distillation. The specific steps are as follows:

[0009] The reaction solution is filtered and dehydrated to remove solid impurities and free water, yielding a pretreated feed solution. The feed solution contains ≥95% total CHDM by mass, with cis-CHDM at 15%–40% and trans-CHDM at 60%–85%. Imidazole ionic liquid is used as the extractant. The pretreated feed solution and the imidazole ionic liquid are continuously fed into an extractive distillation column. The pretreated feed solution is fed from the middle of the column, while the extractant is fed from the top. A light component with a high cis-CHDM content is obtained at the top of the column, while a mixture of trans-CHDM and the extractant is obtained at the bottom. This bottom mixture is then sent to a solvent recovery column for distillation separation to obtain the trans-CHDM product and the recovered imidazole ionic liquid. The recovered imidazole ionic liquid is dehydrated and recycled.

[0010] Further, the imidazole ionic liquid is one or a mixture of 1-allyl-3-methylimidazolium bromide ([Amim]Br), 1-butyl-3-methylimidazolium acetate ([BMIM][Ac]), and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][NTf2]), preferably [BMIM][Ac] and [Amim]Br are mixed at a mass ratio of 1:0.3~0.8. The extractant is dehydrated before use, and the moisture content is ≤0.1% by mass.

[0011] Furthermore, in step 1, the dehydration treatment adopts molecular sieve dehydration method, with 3A or 4A molecular sieves used, the dehydration temperature is 25~40℃, and the dehydration time is 2~4h, to ensure that the water mass fraction in the pretreated raw material liquid is ≤0.05%, so as to avoid water affecting the separation performance of the extractant and the purity of the product.

[0012] Furthermore, the mass ratio of extractant to feed liquid is 1.2~3.5:1; the operating conditions of the extractive distillation column are controlled as follows: top pressure 0.08~0.12MPa, top temperature 180~220℃, bottom temperature 240~280℃, reflux ratio 1.5~4.0, and the number of theoretical plates in the column is 25~45.

[0013] Furthermore, the extractive distillation column is a stainless steel packed column, with Pall rings or stepped rings as the packing material, and the packing specifications are Φ25~Φ50mm, to ensure sufficient gas-liquid contact and improve separation efficiency.

[0014] Furthermore, the extraction and refining tower adopts a continuous feeding method, with a feed liquid flow rate of 50~200 kg / h and an extractant flow rate of 60~700 kg / h, which is suitable for the needs of industrial-scale production.

[0015] Furthermore, the pressure at the top of the solvent recovery tower is controlled at 0.05~0.08MPa, the temperature at the top of the tower is 220~260℃, and the temperature at the bottom of the tower is 280~320℃. Beneficial effects

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] High separation efficiency and significantly improved trans ratio of the product: This invention uses imidazole ionic liquid as the extractant. This type of extractant has excellent selectivity for cis-trans isomers of CHDM and can effectively increase the relative volatility of cis-trans isomers. It solves the technical problem of difficult separation of cis-trans isomers in the prior art. Through extractive distillation process, CHDM products with a trans ratio of up to 85% or more can be obtained directly, which far exceeds the existing foreign industry index of ≥68%. The product quality is better and can be directly applied to the production of high-end polyester to improve the performance of downstream products.

[0018] Green and environmentally friendly with low energy consumption: Imidazole ionic liquids have extremely low vapor pressure, no volatile pollution, and can be recycled up to 8 times, which greatly reduces solvent consumption and environmental pollution. Compared with ordinary distillation, energy consumption is reduced by 30% to 50%, which is in line with the trend of green chemical development. At the same time, it avoids the defects of complex operation and long cycle of crystallization, and is suitable for large-scale continuous production.

[0019] The process is simple and easy to operate: The process steps of this invention are clear, and the pretreatment, extraction distillation, solvent recovery and other links are easy to achieve industrial control. The equipment investment cost is moderate. Compared with gas chromatography separation method, it can realize large-scale industrial purification and solve the problem of insufficient scale of CHDM purification in the existing technology. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the extraction, distillation and purification of CHDM according to the present invention. Detailed Implementation

[0021] Example 1: Extraction and distillation purification of high trans-CHDM using a single [BMIM][Ac] ionic liquid

[0022] 100 kg of the post-reaction CHDM mixture was weighed as raw material. The total mass fraction of CHDM in this raw material was 96.2%, the mass fraction of cis-CHDM was 32.5%, and the mass fraction of trans-CHDM was 63.7%. The raw material was first filtered to remove solid impurities, and then 3A molecular sieve was added. The mixture was then heated at 30°C. oDehydration at constant temperature for 3 hours under C conditions yielded a pretreated feed solution with a water content of only 0.03% by mass. 1-Butyl-3-methylimidazolium acetate ([BMIM][Ac]) was selected as the single extractant and placed in a dedicated dehydration device at 120°C. o C. Dehydrate the extractant under a vacuum of 0.05 MPa for 2 hours to control the water content of the extractant at 0.08%. The pretreated feed solution is continuously fed into the middle of a stainless steel extractive distillation column with 35 theoretical plates and Φ38 mm Pall rings at a flow rate of 80 kg / h. The dehydrated extractant is continuously fed into the top of the same column at a flow rate of 160 kg / h, maintaining a extractant-to-feed solution mass ratio of 2:1. Simultaneously, the process parameters of the extractive distillation column are adjusted, maintaining the top pressure at 0.1 MPa and the top temperature at 200°C. o C, temperature at the bottom of the tower: 260°C o C, reflux ratio 2.5; The light component with a high content of cis-CHDM is separated at the top of the extractive distillation column, and a mixture of trans-CHDM and extractant is discharged from the bottom. This mixture is sent to a solvent recovery column with 20 theoretical plates, and the pressure at the top of the solvent recovery column is controlled at 0.06 MPa, and the top temperature is 240°C. o C, temperature at the bottom of the tower 300 o C, reflux ratio 1.8, separation of product and extractant is achieved through distillation.

[0023] Experimental results: The trans ratio of the product reached 86.3%, the total purity of CHDM was as high as 99.6%, the product purity met the expected indicators, and the separation effect was stable.

[0024] Example 2: Purification of high trans-CHDM by extraction and distillation of [Amim]Br and [HMIM][NTf2] compound ionic liquid.

[0025] 150 kg of the post-reaction CHDM mixture was weighed as raw material, with a total CHDM mass fraction of 95.8%, a cis-CHDM mass fraction of 28.6%, and a trans-CHDM mass fraction of 67.2%. The raw material was first filtered to remove solid impurities, and then 4A molecular sieve was added. The mixture was then heated at 35°C. o Dehydration was carried out at a constant temperature of 130°C for 2.5 hours. A mixed extractant was prepared by combining 1-allyl-3-methylimidazolium bromide ([Amim]Br) and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIM][NTf2]) at a mass ratio of 1:0.5. The mixed extractant was placed in a dehydration device and dehydrated at 130°C. oC. Dehydrate under a vacuum of 0.06 MPa for 1.5 h to control the water content of the extractant at 0.09% by mass. The pretreated feed solution is continuously fed into the middle of a stainless steel extractive distillation column with 40 theoretical plates and Φ50 mm stepped ring packing at a flow rate of 120 kg / h. The compound extractant is continuously fed from the top of the column at a flow rate of 288 kg / h. The extractant to feed solution mass ratio is 2.4:1. The operating parameters of the extractive distillation column are adjusted as follows: top pressure 0.11 MPa, top temperature 210 °C. o C, temperature at the bottom of the tower: 270 o C, reflux ratio 3.0; the light component with a cis-CHDM mass fraction of 71.5% is collected from the top of the column, and the bottom mixture is fed into a solvent recovery column with 22 theoretical plates. The pressure at the top of the solvent recovery column is controlled at 0.07 MPa, and the top temperature is 250°C. o C, temperature at the bottom of the tower: 310 o C, reflux ratio 2.0, after distillation separation, trans-CHDM product and recovered extractant are obtained.

[0026] Experimental results: The trans-CHDM product had a trans ratio of 87.8% and a total CHDM purity of 99.7%. The compound extractant showed better selectivity, and the product purity and trans ratio were further improved compared with the single extractant, with good separation accuracy.

[0027] Example 3: Purification of high trans-CHDM using a compound extractant with an optimized ratio of [BMIM][Ac] and [Amim]Br

[0028] 200 kg of the post-reaction CHDM mixture was weighed as raw material. The total mass fraction of CHDM in this raw material was 97.1%, with cis-CHDM at 19.8% and trans-CHDM at 77.3%. Solid impurities were first removed by filtration, then 3A molecular sieve was added, and the mixture was dehydrated at 28℃ for 3.5 h to prepare a pretreated raw material solution with a moisture content of only 0.02%. 1-Butyl-3-methylimidazolium acetate ([BMIM][Ac]) and 1-allyl-3-methylimidazolium bromide ([Amim]Br) were selected at a mass ratio of 1:0.7 as the extractant. This mixed extractant was dehydrated at 110℃ and 0.04 MPa vacuum for 2.5 h to control the moisture content at 0.06%. The pretreated feed liquid was continuously fed into the middle of a stainless steel extractive distillation column with 30 theoretical plates and Φ25mm Pall rings at a flow rate of 180 kg / h. The compound extractant was continuously fed into the top of the column at a flow rate of 396 kg / h. The mass ratio of extractant to feed liquid was 2.2:1. The parameters of the extractive distillation column were controlled as follows: top pressure 0.09 MPa, top temperature 190℃, bottom temperature 250℃, and reflux ratio 2.0. A light component with a mass fraction of 69.7% cis-CHDM was collected from the top of the column. The bottom mixture was sent to a solvent recovery column with 18 theoretical plates. The top pressure of the solvent recovery column was controlled as 0.05 MPa, top temperature 230℃, bottom temperature 290℃, and reflux ratio 1.5. After distillation separation, the trans-CHDM product was obtained.

[0029] Experimental results: The trans-CHDM product had a trans ratio as high as 89.2% and a total CHDM purity of 99.8%. The product purity and trans ratio were the best among the three examples. The extractant circulation performance was stable, fully meeting the production requirements of high-purity, high-trans-CHDM.

Claims

1. A method for extractive distillation purification of high trans-1,4-cyclohexanediethanol from a terephthalic acid ester hydrogenation reaction solution, characterized in that, Using a hydrogenation reaction solution of terephthalic acid esters containing cis-1,4-cyclohexanediethanol and trans-1,4-cyclohexanediethanol as raw material, and imidazole ionic liquid as extractant, the separation of cis and trans isomers is achieved through extractive distillation. Specific steps include: 1) filtering and dehydrating the reaction solution to remove solid impurities and free water, obtaining a pretreated feed solution. The pretreated feed solution contains a total CHDM mass fraction ≥95%, a cis-CHDM mass fraction of 15%~40%, and a trans-CHDM mass fraction of 60%~85%; 2) continuously feeding the pretreated feed solution from step 1) and the dehydrated imidazole ionic liquid into an extractive distillation column. The pretreated feed solution is fed from the middle of the extractive distillation column, and the extractant is fed from the top. A light component with a high cis-CHDM content is obtained at the top of the extractive distillation column, and a mixture of trans-CHDM and the extractant is obtained at the bottom; 3) [The text abruptly ends here, likely due to an incomplete sentence or missing information.] The bottom mixture is fed into a solvent recovery tower, where it is separated by distillation to obtain trans-CHDM products and recovered imidazole ionic liquids. The recovered imidazole ionic liquids are then dehydrated and recycled.

2. The purification method according to claim 1, characterized in that, The imidazole ionic liquid is one or a mixture of 1-allyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium acetate, and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; preferably, 1-butyl-3-methylimidazolium acetate and 1-allyl-3-methylimidazolium bromide are mixed at a mass ratio of 1:0.3~0.8; the imidazole ionic liquid is dehydrated before use, and the moisture content is ≤0.1% by mass.

3. The purification method according to claim 1, characterized in that, In step 1), the dehydration treatment adopts molecular sieve dehydration method, the molecular sieve is 3A or 4A molecular sieve, the dehydration temperature is 25~40℃, the dehydration time is 2~4h, and the water mass fraction in the pretreated raw material liquid is ≤0.05%.

4. The purification method according to claim 1, characterized in that, In step 2), the mass ratio of extractant to pretreated feed liquid is 1.2~3.5:1; the operating conditions of the extractive distillation column are: top pressure 0.08~0.12MPa, top temperature 180~220℃, bottom temperature 240~280℃, reflux ratio 1.5~4.0, and the number of theoretical plates in the column is 25~45.

5. The purification method according to claim 1, characterized in that, The extraction distillation column is a stainless steel packed column, and the packing is selected from Pall rings or stepped rings, with a packing specification of Φ25~Φ50mm.

6. The purification method according to claim 1, characterized in that, In step 2), the extractive distillation column adopts a continuous feeding method, with the feed flow rate of the pretreated raw material liquid being 50~200 kg / h and the feed flow rate of the extractant being 60~700 kg / h.

7. The purification method according to claim 1, characterized in that, In step 3), the operating conditions of the solvent recovery tower are: top pressure 0.05~0.08MPa, top temperature 220~260℃, and bottom temperature 280~320℃.

8. The purification method according to claim 1, characterized in that, Step 3) The total purity of the trans-CHDM product obtained is ≥90%.

Images