Separation and purification method for recovering 2, 6-diisopropylnaphthalene from low-concentration crystallization waste liquid

Abstract

The invention discloses a separation and purification method for recovering 2, 6-diisopropylnaphthalene from low-concentration crystallization waste liquid, which comprises the following steps: pre-separating the crystallization waste liquid containing 2, 6-diisopropylnaphthalene to separate 1, 3-diisopropylnaphthalene and 1, 7-diisopropylnaphthalene light components, so as to obtain an intermediate component containing 2, 6-diisopropylnaphthalene; the method comprises the following steps: carrying out static melt crystallization on an intermediate component containing 2, 6-diisopropylnaphthalene, crystallizing, sweating and melting to obtain a crude 2, 6-diisopropylnaphthalene crystal and a primary crystallization mother solution; and carrying out solution crystallization on the crude 2, 6-diisopropyl naphthalene crystal to obtain the purified 2, 6-diisopropyl naphthalene crystal. The method well solves the problem of separation and recovery of low-concentration 2, 6-diisopropylnaphthalene in the prior art, has low equipment requirements and low energy consumption, and is beneficial to industrial production of 2, 6-diisopropylnaphthalene.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry and relates to a separation and purification method for recovering 2,6-diisopropylnaphthalene from low-concentration crystal waste liquid. Background Art

[0002] Diisopropylnaphthalene (DIPN) is an important organic chemical raw material with the characteristics of high boiling point, low melting point, colorless, odorless, low toxicity, good biodegradability, and appropriate viscosity. It has received extensive attention and application in the fields of environment and chemical industry. For example, diisopropylnaphthalene mixtures are used as solvents for high-quality copy materials, plant growth regulators, and a new generation of high-temperature synthetic heat transfer oils. The most promising application is 2,6-diisopropylnaphthalene (2,6-DIPN), which can be used to prepare high-value-added polymer materials such as polyethylene naphthalate (PEN) through oxidation, esterification, and polymerization. Due to the high symmetry of 2,6-DIPN, PEN has the characteristics of a straight-chain polymer. At the same time, because the rigidity of the naphthalene ring is greater than that of the benzene ring, the polymer obtained from naphthalene aromatics has better performance. Compared with the widely used polyethylene terephthalate (PET), PEN has better physical and mechanical properties, heat resistance, gas barrier properties, and UV protection properties as shown in Table 1. It can be used to make ultra-thin video substrates, F-class insulation films, high-performance electronic components, food packaging films, hollow molding and high-temperature resistant industrial yarns, etc. Naphthalene polymers are the development trend of engineering plastics in the future.

[0003] Diisopropylnaphthalene can be obtained by reacting naphthalene with propylene or isopropanol. The isopropylation reaction of naphthalene is a series of reactions, which will produce various isomers with different alkylation levels, such as monoisopropylnaphthalene (MIPN), diisopropylnaphthalene (DIPN), and triisopropylnaphthalene (TIPN). There are 8 hydrogen atoms on the naphthalene ring that can be replaced, and theoretically 10 disubstituted isomers can be produced. In order to meet the high purity (>95%) requirements of 2,6-naphthalenedicarboxylic acid production, 2,6-DIPN must be separated and purified. MIPN, DIPN and TIPN can be separated by conventional distillation. However, the physical and chemical properties of various isomers of DIPN are very similar. As shown in Table 2, their boiling points are between 308.6℃ and 319.6℃. The boiling points of 2,6-DIPN and 2,7-DIPN are 319.6℃ and 317.0℃, respectively, with a difference of only 2℃ between the two boiling points. Moreover, eutectics are easily produced during crystallization, causing impurities to precipitate together, which makes it extremely difficult to directly separate DIPN.

[0004] The Chinese patent "Method for Purifying 2,6-Diisopropylnaphthalene" (patent application number 201610831245.8) proposes a crystallization method for purifying 2,6-diisopropylnaphthalene. This method also pre-separates the original sample, and then separates and purifies 2,6-diisopropylnaphthalene through two-stage suspension melt crystallization. However, compared with this scheme, there are the following main shortcomings: 1) It is difficult to apply to samples with large isomer contents such as 2,7-diisopropylnaphthalene and 1,3-diisopropylnaphthalene. These isomers will increase the difficulty of crystallization or form eutectics. 2) The initial 2,6-diisopropylnaphthalene concentration is required to be high, and most of the crystallization mother liquor cannot be recycled. 3) During the melt crystallization process, the mother liquor containing impurities will be entrained between the crystals, which is difficult to wash. Summary of the invention

[0005] In view of the problems in the prior art that the concentration of 2,6-diisopropylnaphthalene in the raw material is high and the product purity is low, the purpose of the present invention is to provide a separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid. The method solves the problem of separation and recovery of low-concentration 2,6-diisopropylnaphthalene, has low requirements on equipment and low energy consumption, and is conducive to the industrial production of 2,6-diisopropylnaphthalene.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid comprises the following steps: Pre-separating the crystallization waste liquid containing 2,6-diisopropylnaphthalene to separate 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene light components to obtain an intermediate component containing 2,6-diisopropylnaphthalene; The intermediate component containing 2,6-diisopropylnaphthalene is subjected to static melt crystallization, and crude 2,6-diisopropylnaphthalene crystals and primary crystallization mother liquor are obtained through crystallization, sweating and melting; The crude 2,6-diisopropylnaphthalene crystals are subjected to solution crystallization to obtain purified 2,6-diisopropylnaphthalene crystals.

[0007] A further improvement of the present invention is that the mass concentration of 2,6-diisopropylnaphthalene in the crystallization waste liquid is 10% to 20%.

[0008] A further improvement of the present invention is that the crystallization waste liquid also includes 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene, the mass concentration of 1,3-diisopropylnaphthalene is 14% to 20%, and the mass concentration of 1,7-diisopropylnaphthalene is 15% to 20%.

[0009] A further improvement of the present invention is that the pressure of the pre-separation vacuum distillation tower is 100Pa~1000Pa, more preferably 100Pa~500Pa; the number of plates of the vacuum distillation tower is 20~50, more preferably 30~40, and the reflux ratio is preferably 1:1~1:3.

[0010] A further improvement of the present invention is that the mass concentration of 2,6-diisopropylnaphthalene in the intermediate component containing 2,6-diisopropylnaphthalene is 22% to 35%, the mass concentration of 1,3-diisopropylnaphthalene is 0% to 10%, and the mass concentration of 1,7-diisopropylnaphthalene is 0% to 15%.

[0011] A further improvement of the present invention is that the minimum temperature of static melt crystallization is -30°C to -10°C, the crystallization time at the minimum temperature is 12h to 48h; the termination temperature is 40°C to 65°C, and the temperature is raised to the termination temperature and maintained for 0.5h to 3h; The mass concentration of 2,6-diisopropylnaphthalene in the crude 2,6-diisopropylnaphthalene crystals is 70%~90%.

[0012] A further improvement of the present invention is that the heating rate of static melt crystallization is 0.2°C / min-0.3°C / min.

[0013] A further improvement of the present invention is that part of the mother liquor from the solution crystallization is used for pre-separation after the ethanol is removed from the recovery distillation tower.

[0014] A further improvement of the present invention is that the temperature of solution crystallization is 10°C to 40°C and the solvent used is ethanol.

[0015] A further improvement of the present invention is that the mass ratio of crude 2,6-diisopropylnaphthalene crystals to ethanol is 1:2 to 1:5; The mass concentration of 2,6-diisopropylnaphthalene in the purified 2,6-diisopropylnaphthalene crystals is 98.5%~99.9%.

[0016] Compared with the existing methods, the present invention mainly has the following beneficial effects: In the present invention, 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene are removed in the pre-separation operation, so that subsequent crystallization can be carried out under conditions close to room temperature, saving a lot of energy costs, while reducing the number of isomers to make crystallization easier to form, reducing crystallization time and improving production efficiency. The present invention has low requirements for raw materials, and can use the remaining crystallization waste liquid in the traditional separation method as a raw material, allowing the presence of a large amount of other isomers such as 1,3-diisopropylnaphthalene. The present invention can separate samples in which 2,6-diisopropylnaphthalene accounts for less than 20% of diisopropylnaphthalene, greatly reducing the requirements for raw material purity, overcoming the problem that conventional separation methods are directed to the direct product after isopropylation of naphthalene, and have certain requirements for the ratio of each isomer of diisopropylnaphthalene (the proportion of 2,6-diisopropylnaphthalene is often around 40%). The equipment requirements used in the method are simple, requiring only simple distillation equipment, and simple-to-operate static melt crystallization equipment, etc., and it is easier to achieve continuous operation.

[0017] Furthermore, a large amount of mother liquor remaining from the crystallization can be recycled, which greatly improves the yield and saves the cost of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structure of the device used in the separation and purification method of the present invention; Figure 2 The GC spectrum of 2,6-diisopropylnaphthalene obtained by the separation and purification method of the present invention; In the figure, 1 is a vacuum distillation tower, 2 is a static melt crystallizer, 3 is a solution suspension crystallizer, 4 is a centrifuge, and 5 is a recovery distillation tower. DETAILED DESCRIPTION

[0019] The present invention will be described more fully below in conjunction with the embodiments. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0020] The crystallization waste liquid targeted by the present invention contains 8 diisopropylnaphthalene isomers.

[0021] The invention aims at the problems in the prior art that the concentration of 2,6-diisopropylnaphthalene in the raw material is high, the product purity is low, the 2,6-diisopropylnaphthalene in the mother liquor is difficult to recover, and impurities interfere with crystallization. The invention provides a separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid. The method adopts a static melt crystallization method and a solution crystallization method to produce high-purity 2,6-diisopropylnaphthalene. The crystallization waste liquid is pre-separated by rectification to separate lighter isomers such as 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene, and a mixed liquid containing a small amount of 2,6-diisopropylnaphthalene and composed of several diisopropylnaphthalene isomers is obtained as a crystallization raw material. The first-stage static melt crystallization is performed to obtain 2,6-diisopropylnaphthalene with lower purity. The product is further purified by second and third-stage solution crystallizations, and finally 2,6-diisopropylnaphthalene crystals are obtained after washing and drying. The technical solution adopted by the present invention effectively solves the problem of separation and recovery of low-concentration 2,6-diisopropylnaphthalene in the existing technology, and at the same time has low requirements on equipment and low energy consumption, which is conducive to the industrial production of 2,6-diisopropylnaphthalene.

[0022] See also Figure 1 The device used in the separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid includes a vacuum distillation tower 1, a static melt crystallizer 2, a solution suspension crystallizer 3, a centrifuge 4 and a recovery distillation tower 5, the bottom of the vacuum distillation tower 1 is connected to the inlet of the static melt crystallizer 2, the outlet of the static melt crystallizer 2 is connected to the solution suspension crystallizer 3, the solution suspension crystallizer 3 is connected to the centrifuge 4, the centrifuge 4 is connected to the recovery distillation tower 5, and the recovery distillation tower 5 is connected to the solution suspension crystallizer 3.

[0023] Specifically, a separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid of the present invention comprises the following steps: a) the crystallization waste liquid containing a small amount of 2,6-diisopropylnaphthalene is pre-separated through a vacuum distillation tower 1 to separate 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene light components to obtain an intermediate component containing 2,6-diisopropylnaphthalene; Wherein, excluding the solvent, the mass concentration of 2,6-diisopropylnaphthalene in the crystallization waste liquid is 10% to 20%, preferably 14% to 20%.

[0024] The mass concentration of 1,3-diisopropylnaphthalene in the crystallization waste liquid is 14%~20%, and the mass concentration of 1,7-diisopropylnaphthalene is 15%~20%.

[0025] The pressure of the vacuum distillation tower is 100Pa~1000Pa, more preferably 100Pa~500Pa; the number of plates of the vacuum distillation tower is 20~50, more preferably 30~40, and the reflux ratio is preferably 1:1~1:3.

[0026] The mass concentration of 2,6-diisopropylnaphthalene in the intermediate component containing 2,6-diisopropylnaphthalene is 22%~35%, the mass concentration of 1,3-diisopropylnaphthalene is 0%~10%, and the mass concentration of 1,7-diisopropylnaphthalene is 0%~15%.

[0027] b) The intermediate component containing 2,6-diisopropylnaphthalene is placed in a primary crystallizer (i.e., static melt crystallizer 2) for static melt crystallization, and crude 2,6-diisopropylnaphthalene crystals and primary crystallization mother liquor are obtained through crystallization, sweating, and melting. The mass concentration of 2,6-diisopropylnaphthalene in the crude 2,6-diisopropylnaphthalene crystals is 70% to 90%.

[0028] The minimum temperature of the primary crystallizer is -30°C to -10°C, more preferably -30°C to -20°C, and the crystallization time at the minimum temperature is preferably 12h to 48h, more preferably 18h to 24h; the termination temperature is preferably 40°C to 65°C, more preferably 50 to 60°C, and the temperature is raised to the termination temperature and maintained for preferably 0.5h to 3h, more preferably 1h to 2h.

[0029] The melt heating rate of the primary crystallizer is preferably 0.2°C / min-0.3°C / min, more preferably 0.2°C / min-0.25°C / min.

[0030] After the mother liquor of the primary crystallizer flows out, the system is heated to above 80° C., and the crude 2,6-diisopropylnaphthalene melts and flows out.

[0031] c) Dissolve the crude 2,6-diisopropylnaphthalene crystals in ethanol at 50°C to 70°C, and enter the secondary crystallizer (solution suspension crystallizer 3) for solution crystallization. After passing through the solid-liquid separator 4, 2,6-diisopropylnaphthalene crystals and secondary crystallization mother liquor are obtained. The 2,6-diisopropylnaphthalene crystals are washed with ethanol at -10°C to 20°C and dried as the final product. The mass concentration of 2,6-diisopropylnaphthalene in the final product is 98.5% to 99.9%. Part of the mother liquor of the secondary crystallizer can be returned to the primary crystallizer after removing the ethanol through the recovery distillation tower 5.

[0032] Among them, the temperature of the secondary crystallizer is 10℃~40℃.

[0033] The mass ratio of the low-purity 2,6-diisopropylnaphthalene crystals to the solvent ethanol in the solution of the secondary crystallizer is 1:2-1:5, more preferably 1:3-1:5.

[0034] The following are specific embodiments.

[0035] Example 1 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 30 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 28% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -20°C and a crystallization time of 12h. It is then heated to 55°C at a heating rate of 0.2°C / min and maintained for 1.5h to obtain diisopropylnaphthalene with a purity of 87.9%. The crude crystals are dissolved in 4 times the mass of ethanol at 60°C and enter the secondary crystallizer for crystallization, with a temperature of 20°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 99.6%.

[0036] See also Figure 2 , the first peak is the solvent peak, and the second peak is 2,6-diisopropylnaphthalene.

[0037] Example 2 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 30 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 28% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -20℃ and a crystallization time of 12 h. It is then heated to 45℃ at a heating rate of 0.2℃ / min and maintained for 1.5h to obtain diisopropylnaphthalene with a purity of 74.9%. The crude crystals are dissolved in 4 times the mass of ethanol at 60℃ and enter the secondary crystallizer for crystallization, with a temperature of 20℃ and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 98.6%.

[0038] Example 3 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 30 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 28% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -20°C and a crystallization time of 12h. It is then heated to 55°C at a heating rate of 0.2°C / min and maintained for 1.5h to obtain diisopropylnaphthalene with a purity of 87.9%. The crude crystals are dissolved in 4 times the mass of methanol at 60°C and enter the secondary crystallizer for crystallization, with a temperature of 20°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C methanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 99.3%.

[0039] Example 4 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 10 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 22% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -25°C and a crystallization time of 48h. It is then heated to 55°C at a heating rate of 0.2°C / min and maintained for 1.5h to obtain diisopropylnaphthalene with a purity of 85.5%. The crude crystals are dissolved in 4 times the mass of ethanol at 60°C and enter the secondary crystallizer for crystallization, with a temperature of 20°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 99.5%.

[0040] Example 5 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 30 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 28% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -20°C and a crystallization time of 12h. It is then heated to 55°C at a heating rate of 0.2°C / min and maintained for 1.5h to obtain diisopropylnaphthalene with a purity of 87.9%. The crude crystals are dissolved in 5 times the mass of ethanol at 50°C and enter the secondary crystallizer for crystallization, with a temperature of 20°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 99.8%.

[0041] Example 6 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 14% 2,6-diisopropylnaphthalene, 15% 1,3-diisopropylnaphthalene, 15% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 40 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 25% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -30°C and a crystallization time of 18h. It is then heated to 60°C at a heating rate of 0.3°C / min and maintained for 0.5h to obtain diisopropylnaphthalene with a purity of 85.4%. The crude crystals are dissolved in 5 times the mass of ethanol at 70°C and enter the secondary crystallizer for crystallization, with a temperature of 30°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried to obtain a final 2,6-diisopropylnaphthalene product with a purity of 99.4%.

[0042] Example 7 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 20% ​​2,6-diisopropylnaphthalene, 17% 1,3-diisopropylnaphthalene, 20% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 35 plates, and a reflux ratio of 1:2. The bottom of the tower obtains an intermediate component containing 30% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -10℃ and a crystallization time of 24h. It is then heated to 50℃ at a heating rate of 0.25℃ / min and maintained for 3h to obtain diisopropylnaphthalene with a purity of 89.3%. The crude crystals are dissolved in ethanol of twice the mass at 60℃ and enter the secondary crystallizer for crystallization, with a temperature of 40℃ and a crystallization time of 1h. After solid-liquid separation, the mother liquor is distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals are washed with 0°C ethanol and then vacuum dried to obtain a final 2,6-diisopropylnaphthalene product with a purity of 99.8%.

[0043] Example 8 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 16% 2,6-diisopropylnaphthalene, 20% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 33 plates, and a reflux ratio of 1:3. The bottom of the tower obtains an intermediate component containing 24% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -20°C and a crystallization time of 48h. It is then heated to 53°C at a heating rate of 0.3°C / min and maintained for 2 h to obtain diisopropylnaphthalene with a purity of 84.8%. The crude crystals are dissolved in 3 times the mass of ethanol at 55°C and enter the secondary crystallizer for crystallization, with a temperature of 10°C and a crystallization time of 1h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried to obtain the final 2,6-diisopropylnaphthalene product with a purity of 98.8%.

[0044] Comparative Example 1 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. It enters the vacuum distillation tower for pre-separation, with a tower pressure of 500Pa, 30 plates, and a reflux ratio of 1:1. The bottom of the tower obtains an intermediate component containing 28% 2,6-diisopropylnaphthalene. This component enters the primary crystallizer for suspended melt crystallization, with a crystallization temperature of -15°C and a crystallization time of 8h. The intermediate component with a mass concentration of 40.5% of 2,6-diisopropylnaphthalene is filtered and dissolved in 4 times the mass of ethanol at 60°C. It enters the secondary crystallizer for crystallization, with a temperature of 0°C and a crystallization time of 4h. After solid-liquid separation, the mother liquor was distilled to remove ethanol and then partially refluxed to the primary crystallizer. The crystals were washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product was 81.8%.

[0045] Comparative Example 2 The crystallization waste liquid contains 8 kinds of diisopropylnaphthalenes, including 19% 2,6-diisopropylnaphthalene, 14% 1,3-diisopropylnaphthalene, 17% 1,7-diisopropylnaphthalene, and 2,7-diisopropylnaphthalene, by mass percentage. This component enters the primary crystallizer for static melt crystallization, with a crystallization temperature of -40°C and a crystallization time of 48h. It is then heated to 53°C at a heating rate of 0.3°C / min and maintained for 2h to obtain diisopropylnaphthalene with a purity of 76.5%. It is dissolved in 4 times the mass of ethanol at 60°C and enters the secondary crystallizer for crystallization at a temperature of 0°C and a crystallization time of 4h. After solid-liquid separation, the mother liquor is distilled to remove ethanol and partially refluxed to the primary crystallizer. The crystals are washed with 0°C ethanol and then vacuum dried. The purity of the final 2,6-diisopropylnaphthalene product is 97.8%.

[0046] By comparing Examples 1-5 with Comparative Example 1, it can be seen that static melt crystallization is easier to obtain high-purity samples than suspended melt crystallization; by comparing Examples 1-5 with Comparative Example 2, it can be seen that the minimum temperature required for static melt crystallization of samples of 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene without pre-separation is significantly lower than that of pretreated samples, which has higher requirements on refrigeration equipment and high energy consumption.

[0047] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid, characterized in that: The following steps are involved: Pre-separating the crystallization waste liquid containing 2,6-diisopropylnaphthalene to separate 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene light components to obtain an intermediate component containing 2,6-diisopropylnaphthalene; The intermediate component containing 2,6-diisopropylnaphthalene is subjected to static melt crystallization, and crude 2,6-diisopropylnaphthalene crystals and primary crystallization mother liquor are obtained through crystallization, sweating and melting; The crude 2,6-diisopropylnaphthalene crystals are subjected to solution crystallization to obtain purified 2,6-diisopropylnaphthalene crystals.

2. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The mass concentration of 2,6-diisopropylnaphthalene in the crystallization waste liquid is 10%~20%.

3. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The crystallization waste liquid also includes 1,3-diisopropylnaphthalene and 1,7-diisopropylnaphthalene. The mass concentration of 1,3-diisopropylnaphthalene is 14%~20%, and the mass concentration of 1,7-diisopropylnaphthalene is 15%~20%.

4. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The pressure of the pre-separation vacuum distillation tower is 100Pa~1000Pa, more preferably 100Pa~500Pa; the number of plates of the vacuum distillation tower is 20~50, more preferably 30~40, and the reflux ratio is preferably 1:1~1:

3.

5. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The mass concentration of 2,6-diisopropylnaphthalene in the intermediate component containing 2,6-diisopropylnaphthalene is 22%~35%, the mass concentration of 1,3-diisopropylnaphthalene is 0%~10%, and the mass concentration of 1,7-diisopropylnaphthalene is 0%~15%.

6. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The lowest temperature of static melt crystallization is -30℃~-10℃, and the crystallization time at the lowest temperature is 12h~48h; the termination temperature is 40℃~65℃, and the time of heating to the termination temperature is 0.5h-3h; The mass concentration of 2,6-diisopropylnaphthalene in the crude 2,6-diisopropylnaphthalene crystals is 70%~90%.

7. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The heating rate of static melt crystallization is 0.2℃ / min-0.3℃ / min.

8. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: Part of the mother liquor from solution crystallization is used for pre-separation after removing ethanol through a recovery distillation tower.

9. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 1, characterized in that: The temperature of solution crystallization is 10°C~40°C, and the solvent used is ethanol.

10. The separation and purification method for recovering 2,6-diisopropylnaphthalene from crystallization waste liquid according to claim 9, characterized in that: The mass ratio of crude 2,6-diisopropylnaphthalene crystals to ethanol is 1:2 to 1:5; The mass concentration of 2,6-diisopropylnaphthalene in the purified 2,6-diisopropylnaphthalene crystals is 98.5%~99.9%.

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