Device and method for preparing dimethyl 2, 6-naphthalate through reactive crystallization

Abstract

The invention provides a device and method for preparing dimethyl 2, 6-naphthalate through reactive crystallization, the device comprises a reactive crystallization kettle and an adsorption dehydration unit, the reactive crystallization kettle is used for carrying out esterification reaction on crude 2, 6-naphthalic acid and methanol to generate the dimethyl 2, 6-naphthalate, and the dimethyl 2, 6-naphthalate is crystallized; the adsorption dehydration unit comprises a storage tank and a condenser, a dehydrating agent is arranged in the storage tank, and the storage tank is provided with a dehydrated steam outlet and a reaction steam inlet; and a dehydration steam pipe is mounted in the dehydration steam outlet. According to the device for preparing dimethyl 2, 6-naphthalate through reactive crystallization, the reactive crystallization kettle is esterification synthesis and crystallization purification integrated equipment, the adsorption dehydration unit can adsorb water generated in esterification reaction, chemical equilibrium can be conducted in the forward direction, use of too many and excessive methanol reactants is avoided, generation of M, M-2, 6-NDC is greatly reduced, and the yield of dimethyl 2, 6-naphthalate is increased. The conversion rate of the reaction is improved.

Description

Technical Field

[0001] This application relates to the field of new coal chemical materials technology, and in particular to an apparatus and method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization. Background Technology

[0002] my country possesses abundant coal reserves. Given the increasingly tight energy situation, developing high-value-added routes for naphthalene is of great significance as a measure to enhance the comprehensive utilization of heavy components in energy sources such as coal and oil. Polyethylene 2,6-naphthalenedicarboxylate (PEN) film is a newly emerging high-performance functional polymer resin material. It is mainly obtained by direct polymerization or transesterification of 2,6-naphthalenedicarboxylic acid (2,6-NDA) or dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) with ethylene glycol, followed by high-temperature, high-vacuum polycondensation. Compared with widely used polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), this polymer material exhibits better airtightness, mechanical properties, dyeing properties, resilience, stain resistance, and chemical stability. Therefore, PEN polyester materials are widely used in fiber textile materials, film materials, packaging materials, engineering plastics, and other fields.

[0003] 2,6-NDA and 2,6-NDC are key monomers in the synthesis of PEN, and their preparation methods include two routes: The first route, direct polymerization of 2,6-NDA, is simple; however, 2,6-NDA has a high melting point of 310°C, a low saturated vapor pressure, and poor solubility in various organic solvents, making efficient purification difficult. The second route involves esterifying crude 2,6-NDA with methanol, followed by purification and transesterification polymerization. This route is more complex than the first and produces methanol as a byproduct. However, 2,6-NDC has a much lower melting point than 2,6-NDA (approximately 190°C), and its solubility in organic solvents is also much greater, allowing for purification through crystallization, distillation, and other methods.

[0004] Currently, the relevant technologies for synthesizing dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) mainly suffer from the following drawbacks: (1) The esterification reaction of 2,6-NDA requires a large amount of methanol. The mass ratio of 2,6-NDA to methanol is at least 1:7.5, and the molar ratio is at least 1:50. This is because the esterification reaction is a reversible reaction limited by chemical equilibrium. In order to improve the conversion rate, the existing ester production process mainly adopts the method of alcohol excess. However, the final product contains a large amount of alcohol, which needs to be separated and recovered. This will undoubtedly increase energy consumption and production costs. In addition, due to the large amount of excess alcohol, the overall utilization efficiency of the reactor is not high.

[0005] (2) The esterification conversion rate of 2,6-NDA needs to be improved. Industrially, the main method is to utilize the formation of an azeotrope between the alcohol and the product or to add components to the system to form an azeotrope with the alcohol and then distill them together, thereby shifting the reaction to the right. However, this also complicates the process and consumes more energy. Furthermore, the distillate needs to be purified and the methanol recovered, which increases the production cost.

[0006] (3) When using esterification-pervaporation membrane technology for synthesis, there are drawbacks such as limited membrane reactor capacity, poor corrosion resistance of membrane materials, and poor repeatability of membrane modules.

[0007] (4) The recrystallization method used in the purification of 2,6-NDC is complicated. It adopts two-stage recrystallization, resulting in large material loss, low yield, large amount of recrystallization solvent consumed, large number of equipment required, and some damage to the ambient air. Summary of the Invention

[0008] In view of this, one objective of this application is to provide an apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization. This apparatus incorporates a reaction crystallization vessel and an adsorption dehydration unit. The reaction crystallization vessel is an integrated device for esterification synthesis and crystallization purification, capable of both esterification synthesis of 2,6-NDC and crystallization purification of the esterification product, significantly reducing equipment usage and avoiding material loss during transfer. The adsorption dehydration unit adsorbs water generated during the esterification reaction, promoting a positive chemical equilibrium and avoiding excessive use of methanol reactants, thus greatly reducing the formation of M,M-2,6-NDC, increasing the reaction conversion rate, and reducing energy consumption for methanol recovery from the filtrate. Furthermore, compared to traditional azeotropic distillation, extractive distillation, and pervaporation esterification dehydration processes, the adsorption dehydration unit does not introduce other reagents, avoids pollution, and offers advantages such as good separation effect, low energy consumption, simple process, convenient operation, and minimal raw material loss.

[0009] Another object of this application is to provide a method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization.

[0010] To achieve the above objectives, the first aspect of this application provides an apparatus for the reaction crystallization preparation of dimethyl 2,6-naphthalenedicarboxylate, comprising: A reaction crystallization vessel is used for the esterification reaction of crude 2,6-naphthalenedicarboxylic acid with methanol to produce dimethyl 2,6-naphthalenedicarboxylic acid and crystallize it; the reaction crystallization vessel has a methanol reflux port, a reaction vapor outlet, a discharge port and an exhaust port; An adsorption dehydration unit includes a storage tank and a condenser. The outer surface of the storage tank is provided with a first jacket. The storage tank contains a dehydrating agent and has a dehydration steam outlet and a reaction steam inlet. A dehydration steam pipe is installed in the dehydration steam outlet. The lower end of the dehydration steam pipe extends to a position near the bottom of the storage tank. The upper end of the dehydration steam pipe is connected to the condenser and the methanol reflux port in sequence. The reaction steam inlet is connected to the reaction steam outlet.

[0011] In some embodiments, the reaction crystallization vessel includes: The housing has the methanol reflux port, the reaction vapor outlet, the discharge port and the exhaust port, and the outer surface of the housing is provided with a second jacket; A refrigerant inlet and a refrigerant outlet are provided. A stirrer is mounted on the housing and includes a motor, a rotating shaft, and a first stirring blade located inside the guide tube.

[0012] In some embodiments, both the second jacket and the guide tube are provided with at least one guide plate.

[0013] In some embodiments, the guide tube is located below the cooling crystallization liquid level.

[0014] In some embodiments, the first impeller is a four-bladed propulsion impeller.

[0015] In some embodiments, the agitator further includes a second agitator; the second agitator is located below the first agitator and extends partially below the guide tube; the second agitator is a rake-type agitator and has multiple through holes in at least a portion of its area.

[0016] In some embodiments, the bottom of the housing is provided with the discharge port, and a discharge valve is installed at the discharge port. The discharge valve includes a downward-expanding discharge valve and a ball valve, with the ball valve connected in series below the downward-expanding discharge valve.

[0017] In some embodiments, the dehydrating agent is filled into the storage tank, and the filling height is xx-xx of the height of the storage tank.

[0018] In some embodiments, the dehydrating agent includes at least one of molecular sieve dehydrating agent, silica gel, and anhydrous calcium chloride, preferably 3A molecular sieve.

[0019] In some embodiments, the size of the dehydrating agent is larger than the size of the air inlet of the dehydrating steam pipe, and the size of the dehydrating agent is larger than the size of the reaction steam inlet.

[0020] In some embodiments, a temperature sensor is installed on the reaction crystallization vessel.

[0021] In some embodiments, the purity of the crude 2,6-naphthalenedicarboxylic acid is 92-95 wt%.

[0022] In some embodiments, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes a filtration unit connected to the discharge port.

[0023] In some embodiments, the filtration unit is a vacuum pump.

[0024] The second aspect of this application discloses a method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, applied to the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization described in this application, comprising: The crude 2,6-naphthalenedicarboxylic acid and methanol were subjected to an esterification reaction in the reaction crystallization vessel under the action of a catalyst; The vapor from the esterification reaction process enters the adsorption and dehydration unit for dehydration and condensation to obtain a dehydrated methanol solution. The dehydrated methanol solution is continuously returned to the reaction crystallization vessel; After the esterification reaction is completed, the adsorption and dehydration unit is turned off, and the product of the esterification reaction is cooled and crystallized.

[0025] In some embodiments, the cooling crystallization includes the following steps: (1) The product of the esterification reaction is subjected to a first cooling; (2) After the first cooling, dimethyl 2,6-naphthalenedicarboxylate and methanol with a purity of more than 99 wt% are added (to introduce seed crystals), followed by a second cooling and heat preservation.

[0026] In some embodiments, the termination temperature of the first cooling is 120-136°C. The termination temperature of the first cooling is also the initial crystallization temperature.

[0027] In some embodiments, in step (2), the mass ratio of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher to the methanol is 6:(70-82), and the amount of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher is 0.5-1.5% of the mass of the crude 2,6-naphthalenedicarboxylate.

[0028] In some implementations, the second cooling method is programmed cooling.

[0029] In some embodiments, the cooling rate of the second cooling is 8-15°C / h.

[0030] In some embodiments, the termination temperature of the second cooling is 28-46°C. The termination temperature of the second cooling is also the final crystallization temperature.

[0031] In some embodiments, the heat preservation time is 0.5-1.5 hours.

[0032] In some embodiments, the esterification reaction is carried out at a temperature of 120-140°C.

[0033] In some embodiments, the reaction pressure of the esterification reaction is 0.8-1.2 MPa.

[0034] In some embodiments, the esterification reaction takes 4-6 hours.

[0035] In some embodiments, the molar ratio of the crude 2,6-naphthalenedicarboxylic acid to methanol involved in the esterification reaction is 1:(27-54).

[0036] In some embodiments, the catalyst comprises concentrated sulfuric acid.

[0037] In some embodiments, the condensation temperature is 35-55°C.

[0038] In some embodiments, the dehydration temperature is 40-60°C.

[0039] In some embodiments, the method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes: After the cooling and crystallization, the reaction crystallization vessel is restored to normal pressure, and then unloaded, filtered, washed, and dried.

[0040] The apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization described in this application can bring at least the following beneficial effects: 1. Due to the inclusion of a reaction crystallization kettle and an adsorption dehydration unit, the reaction crystallization kettle is an integrated device for esterification synthesis and crystallization purification. It can perform both esterification synthesis of 2,6-NDC and crystallization purification of the esterification products, greatly saving equipment usage and avoiding material loss during transfer. The adsorption dehydration unit can adsorb water generated in the esterification reaction, which is conducive to the forward chemical equilibrium and avoids the use of too much methanol reactant, greatly reducing the formation of M,M-2,6-NDC, improving the reaction conversion rate, and reducing the energy consumption of methanol recovery after filtrate treatment. At the same time, compared with traditional azeotropic distillation, extractive distillation, and pervaporation esterification dehydration processes, the adsorption dehydration unit does not introduce other reagents during the process, does not cause pollution, and has the advantages of good separation effect, low energy consumption, simple process, convenient operation, and small raw material loss.

[0041] 2. When molecular sieve dehydrating agents (e.g., 3A molecular sieves) are used as dehydrating agents in the adsorption and dehydration unit, the dehydrating agents can be recycled and reused, which is convenient for industrial scale-up.

[0042] The method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization described in this application, in addition to having the beneficial effects of the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization described in this application, can also bring at least the following beneficial effects: 1. The synthesis and purification of 2,6-NDC using an esterification reaction followed by a single crystallization process involves the use of an integrated reaction and crystallization apparatus (i.e., the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction and crystallization as described in this application). It also enables dehydration during the esterification reaction process. The operation is simple, which can improve purification efficiency, reduce energy consumption, and efficiently and stably obtain high-purity, high-yield 2,6-NDC (wherein the yield reaches more than 95% and the purity can reach 99.95%).

[0043] 2. The reaction crystallization process is adopted, and the parameters of the crystallization process (initial crystallization temperature, cooling rate, introduction of seed crystals, cooling time, final crystallization temperature, etc.) are strictly controlled. There is no need to introduce new methanol solution, and the secondary crystallization operation used in the traditional recrystallization process is omitted, which greatly improves the purification efficiency of 2,6-NDC.

[0044] 3. This method is characterized by its simplicity, high efficiency, and environmental friendliness.

[0045] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0046] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 This is a schematic diagram of an apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, as illustrated in an exemplary embodiment of this application.

[0047] Figure 2 for Figure 1 Enlarged view of point A in the middle.

[0048] Figure 3 This is a flowchart illustrating a method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, as shown in an exemplary embodiment of this application.

[0049] Figure label: 1-Reaction crystallization vessel; 101-Methanol reflux port; 102-Reaction steam outlet; 103-Discharge port; 104-Exhaust port; 105-Shell; 106-Second jacket; 107-Guide tube; 1071-Refrigerant inlet; 1072-Refrigerant outlet; 108-Agitator; 1081-Motor; 1082-Rotating shaft; 1083-First stirring paddle; 1084-Second stirring paddle; 1085-Through hole; 109-Cooling crystallization liquid level; 110-Feed inlet; 111-Spare port; 2-Adsorption dehydration unit; 201-Storage tank; 202-Condenser; 203-First jacket; 204-Dehydrating agent; 205-Dehydration steam outlet; 206-Reaction steam inlet; 207-Dehydration steam pipe; 208-Reflux liquid pipe; 209-Reaction steam pipe. Detailed Implementation

[0050] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0051] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0052] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0053] In this application, atmospheric pressure refers to 1 standard atmosphere (1.01325 × 10⁻⁶). 5 Pa).

[0054] When the term “and / or” is used in a list containing two or more items, it means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression “A and / or B” is intended to mean A or B or A and B, that is, A only, B only, or a combination of A and B.

[0055] The inventors discovered that in the synthesis of dimethyl 2,6-naphthalenedicarboxylate, combining the esterification reaction and crystallization purification process within a single tank significantly reduces equipment usage and avoids material loss during transfer. Simultaneously, effectively removing water generated during the esterification reaction increases the formation of 2,6-NDC diester and reduces the formation of M,M-2,6-NDC monoester, promoting a positive chemical equilibrium and increasing the reaction conversion rate. This also avoids the use of excessive methanol reactants, reducing energy consumption for methanol recovery from the filtrate. Furthermore, the inventors found that by incorporating an adsorption dehydration unit, the aforementioned goal of effectively removing water generated during the esterification reaction can be achieved without introducing other reagents or causing pollution, resulting in good separation performance, low energy consumption, a simple process, convenient operation, and minimal raw material loss.

[0056] The apparatus and method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization according to embodiments of this application are described below with reference to the accompanying drawings.

[0057] Figure 1 This is a schematic diagram of an apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, as illustrated in an exemplary embodiment of this application.

[0058] like Figure 1 As shown, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization according to an embodiment of this application includes a reaction crystallization vessel 1 and an adsorption dehydration unit 2. Wherein, The reaction crystallization vessel 1 is used for the esterification reaction of crude 2,6-naphthalenedicarboxylic acid with methanol to generate dimethyl 2,6-naphthalenedicarboxylic acid and crystallize it; the reaction crystallization vessel 1 has a methanol reflux port 101, a reaction steam outlet 102, a discharge port 103 and an exhaust port 104.

[0059] The adsorption dehydration unit 2 includes a storage tank 201 and a condenser 202. A first jacket 203 is provided on the outer surface of the storage tank 201. During use, a heat exchange medium is introduced into the first jacket to heat the storage tank and thus ensure the dehydration temperature. A dehydrating agent 204 is provided inside the storage tank 201 to remove water vapor from the reaction steam from the reaction steam outlet 102. The storage tank 201 has a dehydration steam outlet 205 and a reaction steam inlet 206. A dehydration steam pipe 207 is installed inside the dehydration steam outlet 205, with its lower end extending to a position near the bottom of the storage tank 201. The upper end of the dehydration steam pipe 207 is sequentially connected to the condenser 202 and the methanol reflux port 101. The reaction steam inlet 206 is connected to the reaction steam outlet 102.

[0060] Understandably, the lower end of the dehydration steam pipe 207 can be infinitely close to the bottom of the storage tank but the two do not contact each other, so that the dehydrated reaction steam can enter the condenser from the dehydration steam pipe for condensation.

[0061] The apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization in this application embodiment incorporates a reaction crystallization vessel and an adsorption dehydration unit. The reaction crystallization vessel is an integrated device for esterification synthesis and crystallization purification, capable of both esterification synthesis of 2,6-NDC and crystallization purification of the esterification product, significantly saving equipment usage and avoiding material loss during transfer. The adsorption dehydration unit adsorbs water generated during the esterification reaction, promoting a positive chemical equilibrium and avoiding the use of excessive methanol reactants, greatly reducing the formation of M,M-2,6-NDC, improving the reaction conversion rate, and reducing energy consumption for methanol recovery and post-treatment of the filtrate. Furthermore, compared to traditional azeotropic distillation, extractive distillation, and pervaporation esterification dehydration processes, the adsorption dehydration unit does not introduce other reagents, avoids pollution, and offers advantages such as good separation effect, low energy consumption, simple process, convenient operation, and minimal raw material loss.

[0062] In some embodiments, the reaction crystallization vessel 1 includes a shell 105, a flow guide tube 107, and a stirrer 108.

[0063] In some embodiments, the housing 105 has the methanol reflux port 101, the reaction vapor outlet 102, the discharge port 103, and the exhaust port 104.

[0064] For example, the methanol reflux port 101, the reaction vapor outlet 102, and the exhaust port 104 are all located at the top of the housing.

[0065] For example, the discharge port 103 is located at the bottom of the housing.

[0066] As an optional example, a discharge valve is installed at the discharge port 103, the discharge valve comprising a downward-expanding discharge valve and a ball valve, the ball valve being connected in series below the downward-expanding discharge valve. This arrangement can prevent a small amount of material leakage from the discharge port.

[0067] In some embodiments, a second jacket 106 is provided on the outer surface of the shell 105 to ensure the temperatures required for the esterification reaction of crude 2,6-naphthalenedicarboxylic acid with methanol and for crystallization. In use, the temperature of the shell can be heated or lowered by introducing heat exchange media of different temperatures into the second jacket to meet the temperatures required for the esterification reaction or crystallization.

[0068] For example, when the esterification reaction is carried out, the heat exchange medium introduced into the second jacket includes, but is not limited to, at least one of water vapor, heat transfer oil, etc., and heat transfer oil can be selected.

[0069] For example, when crystallization is carried out, the heat exchange medium introduced into the second jacket includes, but is not limited to, at least one of deionized water, heat transfer oil, etc., and heat transfer oil can be selected.

[0070] In some embodiments, the flow guide 107 is installed inside the housing 105, and the flow guide 107 has a refrigerant inlet 1071 and a refrigerant outlet 1072.

[0071] In some embodiments, the guide tube 107 is located below the cooling crystallization liquid level 109.

[0072] In some embodiments, at least one guide plate is provided inside both the second jacket 106 and the guide tube 107.

[0073] For example, the heat exchange medium introduced into the first jacket includes, but is not limited to, at least one of deionized water, heat transfer oil, etc.

[0074] In some embodiments, the stirrer 108 is mounted on the housing 105, and the stirrer 108 includes a motor 1081, a rotating shaft 1082 and a first stirring paddle 1083, which is located inside the guide tube 107.

[0075] As an alternative example, the first impeller 1083 is a four-bladed propulsion impeller.

[0076] In some embodiments, the stirrer further includes a second stirring paddle 1084; the second stirring paddle 1084 is located below the first stirring paddle 1083 and extends partially below the guide tube 107; the second stirring paddle 1084 is a rake-type stirring paddle (i.e., a rake), and at least a portion of it is provided with multiple through holes 1085 (e.g., ...). Figure 2 (As shown). This setup improves the internal circulation of the solution, ensuring its uniformity and consistency. It also allows for control over crystal size during crystallization, breaking down and refining the crystals, thereby improving crystallization quality and efficiency.

[0077] For example, the diameter of the through hole 1085 is 15-25mm, preferably 20mm.

[0078] For example, the distance between the edge of the first stirring paddle 1083 and the inner wall of the guide cylinder 107, and the distance between the edge of the second stirring paddle 1084 and the inner wall of the guide cylinder 107 are both 20-40 mm, preferably 30 mm. This arrangement facilitates scraping material from the inner wall of the guide cylinder.

[0079] For example, the second stirring paddle 1084 and the first stirring paddle 1083 are both mounted on a rotating shaft 1082, which is connected to the output shaft of the electrode 1081; the second stirring paddle 1084 is mounted on the bottom of the rotating shaft 1082 and is adjacent to the first stirring paddle 1083.

[0080] In the embodiments of this application, the combined design of the inner wall of the guide tube and the dedicated stirring paddles (i.e., the first and second stirring paddles) results in high heat transfer efficiency, simple configuration, and convenient operation and control, making it suitable for various material crystallization requirements. During the crystallization process, the solution flows into the crystallizer (i.e., the reaction crystallizer) near the bottom of the guide tube and is then conveyed to the liquid surface (i.e., the cooling crystallization liquid level 109) along the guide tube by the slowly rotating stirring paddles. The solution evaporates and cools at the liquid surface, reaching a supersaturated state, and some solute deposits on the surface of the suspended particles, causing crystal growth. Through the dedicated stirring paddle and guide tube design, the guide tube crystallizer (i.e., the reaction crystallizer) can achieve efficient solution mixing and crystal growth, ensuring uniform crystal size.

[0081] Furthermore, the stirrer in the embodiments of this application is generally started and used during the crystallization process, and is not required during the esterification reaction.

[0082] In some embodiments, the dehydrating agent 204 is filled into the storage tank 201 (filled from the bottom of the storage tank 201 upwards).

[0083] In some embodiments, the dehydrating agent 204 includes, but is not limited to, at least one of molecular sieve dehydrating agents, silica gel, anhydrous calcium chloride, etc., preferably a molecular sieve dehydrating agent.

[0084] For example, molecular sieve dehydrating agents include, but are not limited to, at least one of 3A molecular sieve, 4A molecular sieve, 13X molecular sieve, etc., preferably 3A molecular sieve. When a molecular sieve dehydrating agent (e.g., 3A molecular sieve, etc.) is used as the dehydrating agent, the dehydrating agent can be recycled and reused, which is convenient for industrial scale-up.

[0085] In some embodiments, the size of the dehydrating agent is larger than the size of the inlet of the dehydrating steam pipe, and the size of the dehydrating agent is larger than the size of the reaction steam inlet 206. This arrangement prevents the dehydrating agent from being pressure-driven into the reaction crystallization vessel.

[0086] It should be noted that, in the embodiments of this application, the size of the dehydrating agent can be the maximum particle size and / or diameter that prevents it from entering the air inlet and reaction steam inlet of the dehydrating steam pipe; when the cross-section of the air inlet and reaction steam inlet of the dehydrating steam pipe is circular, the size of the air inlet and the size of the reaction steam inlet both refer to their respective diameters; when the cross-section of the air inlet and the reaction steam inlet of the dehydrating steam pipe is square, the size of the air inlet and the size of the reaction steam inlet both refer to the maximum size of their respective cross-sections, such as the length of a rectangle.

[0087] In some embodiments, the reaction steam inlet 206 is connected to the reaction steam outlet 102 via a reaction steam pipe 209, with the reaction steam pipe 209 located at one end of the reaction steam inlet 206 and installed inside the reaction steam inlet 206. In this case, the size of the dehydrating agent is larger than the inlet size of the dehydrating steam pipe, and the size of the dehydrating agent is larger than the inlet size of the reaction steam pipe 209 at one end of the reaction steam inlet 206.

[0088] In some embodiments, a temperature sensor is installed on the reaction crystallization vessel 1.

[0089] In the embodiments of this application, the heating temperature of the shell (i.e., the temperature of esterification reaction and crystallization) is controlled by introducing different heat exchange media into the second jacket. The temperature sensor measures the temperature inside the vessel (i.e., measures the temperature of esterification reaction and crystallization inside the shell) and feeds back the temperature signal, thereby controlling the heating temperature of the shell by the second jacket. The specific process is prior art and will not be described in detail here.

[0090] In some embodiments, the reaction crystallizer 1 also has a feed inlet 110. For example, the feed inlet 110 is located at the top of the housing 105.

[0091] In some embodiments, the reaction crystallization vessel 1 also has at least one spare port 111. Exemplarily, the spare port 111 is located at the top of the housing 105.

[0092] In some embodiments, the condenser 202 and the methanol reflux port 101 are connected by a reflux pipe 208.

[0093] In some embodiments, the purity of the crude 2,6-naphthalenedicarboxylic acid is 92-95 wt%, such as 93 wt%, 94 wt%, or 95%.

[0094] In some embodiments, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes a filtration unit connected to the outlet 103.

[0095] For example, the filtration unit includes, but is not limited to, a vacuum filter pump, a centrifuge, etc., preferably a vacuum filter pump.

[0096] In some embodiments, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes a drying unit.

[0097] For example, the drying unit includes, but is not limited to, an oven, a spray dryer, etc., and may be an oven.

[0098] In some embodiments, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization according to this application further includes various valves installed at various outlets and inlets to control the outflow or inflow of materials or fluids. Specifically, at least some of the valves installed at the reaction steam outlet 102, reaction steam inlet 206, reaction steam pipe 209, methanol reflux port 101, reflux liquid pipe 208, and dehydration steam pipe 207 can be used in combination to shut down the adsorption dehydration unit 2.

[0099] It should be noted that the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization in the embodiments of this application can be used not only to prepare dimethyl 2,6-naphthalenedicarboxylate, but also to prepare diethyl 2,6-naphthalenedicarboxylate, dipropyl 2,6-naphthalenedicarboxylate, etc. In this case, the methanol participating in the esterification reaction needs to be replaced with ethanol, isopropanol, etc. However, the economic efficiency of diethyl 2,6-naphthalenedicarboxylate, dipropyl 2,6-naphthalenedicarboxylate, etc., generated by these alcohols is not as high as that of dimethyl 2,6-naphthalenedicarboxylate generated by methanol participating in the esterification reaction.

[0100] The apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization in this application embodiment can be used in the method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization in this application embodiment.

[0101] Figure 3 This is a flowchart illustrating a method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, as shown in an exemplary embodiment of this application.

[0102] like Figure 3 As shown in the embodiments of this application, the method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization includes the following steps: S101. The crude 2,6-naphthalenedicarboxylic acid and methanol are subjected to an esterification reaction in the reaction crystallization vessel 1 under the action of a catalyst.

[0103] In some embodiments, the reaction temperature of the esterification reaction is 120-140°C, including but not limited to 125°C, 130°C or 135°C, preferably 130°C.

[0104] In some embodiments, the reaction pressure of the esterification reaction is 0.8-1.2 MPa, including but not limited to 0.9 MPa, 1 MPa or 1.1 MPa, preferably 1 MPa.

[0105] In some embodiments, the esterification reaction takes 4-6 hours, for example, 5 hours.

[0106] In some embodiments, the esterification reaction is carried out in air, such as in everyday air.

[0107] In some embodiments, the molar ratio of the crude 2,6-naphthalenedicarboxylic acid to methanol participating in the esterification reaction is 1:(27-54), including but not limited to 1:30, 1:45 or 1:50.

[0108] That is, in the embodiments of this application, the mass ratio of crude 2,6-naphthalenedicarboxylic acid to methanol participating in the esterification reaction is 1:(4-8), for example 1:5 or 1:7.

[0109] In some embodiments, the catalyst includes, but is not limited to, at least one of concentrated sulfuric acid, ferric sulfate, and p-toluenesulfonic acid.

[0110] In some embodiments, the amount of catalyst used is 8-12% of the mass of the crude 2,6-naphthalenedicarboxylic acid participating in the esterification reaction, preferably 10%.

[0111] S102. In step S101, the steam from the esterification reaction process enters the adsorption and dehydration unit 2 for dehydration and condensation to obtain a dehydrated methanol solution.

[0112] In some embodiments, the vapors generated during the esterification process include methanol, water, dimethyl ether, etc.

[0113] In the embodiments of this application, dehydration is carried out in a storage tank and condensation is carried out in a condenser. Specifically, the vapor from the esterification reaction process enters the storage tank 201 from the reaction vapor outlet 102 through the reaction vapor inlet 206, where it is dehydrated by the adsorption of the dehydrating agent 204. Subsequently, the dehydrated vapor enters the condenser 202 through the dehydration vapor outlet 205 for condensation, yielding a dehydrated methanol solution.

[0114] In some embodiments, the dehydration temperature is 40-60°C, including but not limited to 45°C, 50°C or 55°C, preferably 50°C.

[0115] It should be noted that the dehydration temperature is ensured by heating the storage tank with the heat exchange medium introduced into the first jacket.

[0116] In some embodiments, the residence time of the vapor in the storage tank 201 during the esterification reaction is 2-6 minutes, including but not limited to 3 minutes, 4 minutes or 5 minutes.

[0117] In some embodiments, the condensation temperature is 35-55°C, including but not limited to 40°C, 45°C or 50°C, preferably 45°C.

[0118] In some embodiments, the condensation time is 2-5 minutes, including but not limited to 3 minutes or 4 minutes.

[0119] S103. The dehydrated methanol solution obtained in step S102 is continuously returned to the reaction crystallization vessel 1.

[0120] In some embodiments, the dehydrated methanol solution obtained in step S102 is continuously returned to the reaction crystallization vessel 1 via the reflux pipe 208.

[0121] After the esterification reaction described in step S101 is completed, the adsorption and dehydration unit 2 is turned off, and the product of the esterification reaction is cooled and crystallized.

[0122] In some embodiments, the cooling crystallization includes the following steps: (1) The product of the esterification reaction is subjected to a first cooling; (2) After the first cooling, dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) with a purity of more than 99 wt% and methanol are added, followed by a second cooling and heat preservation.

[0123] In the embodiments of this application, the product of the esterification reaction is first cooled down to the critical initial crystallization temperature to ensure a certain degree of saturation and prepare for the subsequent crystallization operation. Then, dimethyl 2,6-naphthalenedicarboxylate and methanol with a purity of more than 99 wt% are added to introduce seed crystals. Finally, a second cooling and holding process is performed to carry out a gradient cooling process, so that the 2,6-NDC crystals precipitate uniformly and the crystals are prevented from growing excessively by temperature control.

[0124] It should be noted that when the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization is used as described above for the preparation of diethyl 2,6-naphthalenedicarboxylate, dipropyl 2,6-naphthalenedicarboxylate, etc., the methanol introduced into the seed crystal in step (2) here also needs to be replaced with ethanol, isopropanol, etc., to be consistent with the selection of alcohols in the esterification reaction.

[0125] In some embodiments, the termination temperature of the first cooling is 120-136°C, including but not limited to 125°C or 130°C, preferably 128°C. The termination temperature of the first cooling is also the initial crystallization temperature. A termination temperature within the above range ensures that the 2,6-NDC in the solution has a certain degree of saturation, preparing for the subsequent crystallization precipitation operation and enabling uniform crystal precipitation after the addition of seed crystals. Below 120°C, the initial crystallization temperature is low, causing 2,6-NDC to precipitate prematurely, resulting in uneven crystal particle size, coating impurities in the solution, and reducing the purity of the final product. Above 130°C, the initial crystallization temperature is high; at this point, the solution is not saturated, and after the addition of seed crystals, the seed crystals dissolve in the methanol solution, failing to play a crystallizing role. The precipitated crystals then cool freely, resulting in uneven particle size, coating impurities in the solution, and reducing the purity of the final product.

[0126] In some embodiments, the purity of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher includes, but is not limited to, 99.5 wt% or higher, 99.7 wt% or higher, or 99.9 wt% or higher.

[0127] In some embodiments, in step (2), the mass ratio of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher to the methanol is 6:(70-82), and the amount of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher is 0.5-1.5% of the mass of the crude 2,6-naphthalenedicarboxylate.

[0128] For example, in step (2), the mass ratio of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher to the methanol includes, but is not limited to, 6:73 or 6:76, preferably 6:76.

[0129] For example, the amount of dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher is 0.75%, 1%, or 1.25% of the mass of the crude 2,6-naphthalenedicarboxylate.

[0130] In some implementations, the second cooling method is programmed cooling.

[0131] In some embodiments, the cooling rate of the second cooling is 8-15°C / h. A cooling rate within this range allows for stable crystal precipitation in the reactor, resulting in larger 2,6-NDC crystals with less encapsulated impurities, high cooling efficiency, and high final product purity. A cooling rate below 8°C / h is too slow, which helps obtain larger crystals but prolongs crystallization time and reduces production efficiency. A cooling rate above 15°C / h is too fast, leading to the formation of fine crystals, causing impurities to be encapsulated within the crystals and reducing crystal purity.

[0132] In some embodiments, the termination temperature of the second cooling is 28-46°C. The termination temperature of the second cooling is also the final crystallization temperature. Within this range, the termination temperature of the second cooling can dissolve M,M-2,6-NDC and other impurities in the solution, resulting in a 2,6-NDC product with high purity, while reducing the loss of 2,6-NDC dissolved in the solution and ensuring a high crystallization yield. Below 28°C, the final crystallization temperature is low, and the crystallization process is too rapid, causing M,M-2,6-NDC and other impurities to precipitate in the solution, ultimately affecting the purity of 2,6-NDC. Above 46°C, the final crystallization temperature is high, the crystallization process is slowed, resulting in the loss of 2,6-NDC dissolved in the solution, and the resulting crystals are smaller in size.

[0133] In some embodiments, the heat preservation time is 0.5-1.5 hours, for example, 1 hour.

[0134] In some embodiments, the method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes: After the cooling and crystallization, the reaction crystallization vessel 1 is restored to normal pressure, and then unloaded, filtered, washed, and dried.

[0135] The method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization according to the embodiments of this application, in addition to having the beneficial effects of the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization according to the embodiments of this application, can also bring at least the following beneficial effects: 1. The synthesis and purification of 2,6-NDC using an esterification reaction followed by a single crystallization process involves the use of an integrated reaction and crystallization apparatus (i.e., the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction and crystallization as described in this application). It also enables dehydration during the esterification reaction process, is simple to operate, improves purification efficiency, reduces energy consumption, and efficiently and stably obtains high-purity, high-yield 2,6-NDC (with a yield of over 95% and a purity of 99.95%).

[0136] 2. The reaction crystallization process is adopted, and the parameters of the crystallization process (initial crystallization temperature, cooling rate, introduction of seed crystals, cooling time, final crystallization temperature, etc.) are strictly controlled. There is no need to introduce new methanol solution, and the secondary crystallization operation used in the traditional recrystallization process is omitted, which greatly improves the purification efficiency of 2,6-NDC.

[0137] 3. This method is characterized by its simplicity, high efficiency, and environmental friendliness.

[0138] The following non-limiting embodiments further illustrate certain features of the present technology.

[0139] All the following embodiments utilize the principles of this application. Figure 2The apparatus shown is used to prepare dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization.

[0140] Example 1 The method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization in this embodiment includes the following steps: (1) Esterification reaction operation: 600g of crude 2,6-NDA (purity 95.0wt%), 3600g of anhydrous methanol and 60g of concentrated sulfuric acid (98.3wt% sulfuric acid) were added to the shell of the reaction crystallization vessel (the mass ratio of 2,6-NDA to anhydrous methanol was 1:6.0, the molar ratio was 1:40.5; the amount of concentrated sulfuric acid catalyst was 10%wt of 2,6-NDA). The esterification reaction was carried out at 130℃, 1.0MPa (gauge pressure) and in air atmosphere for 5 hours. The steam generated during the esterification reaction was discharged from the reaction steam outlet and entered the storage tank of the adsorption and dehydration unit (containing 3A molecular sieve) through the reaction steam inlet. After adsorption and dehydration by the 3A molecular sieve in the storage tank at 50℃ for 4min (that is, the residence time of the reaction steam in the storage tank was 4min), it entered the condenser through the dehydration steam pipe and was condensed at 45℃ for 3min (that is, the residence time of the adsorbed and dehydrated steam in the condenser was 3min) to obtain the dehydrated methanol solution. The dehydrated methanol solution is continuously returned to the shell of the reaction crystallization vessel through the methanol reflux port. After the esterification reaction is completed, the adsorption dehydration unit is shut down to proceed with the crystallization operation.

[0141] (2) Crystallization operation: The reaction crystallizer begins to cool down. When the temperature of the solution inside the reaction crystallizer shell reaches 128°C, a slurry consisting of 6g of 99.99wt% dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) and 76g of anhydrous methanol is pumped into the reaction crystallizer shell through the feed port. The temperature is then reduced to 38.0°C at a rate of 10.0°C / h using a programmed cooling method, and then held at 38°C for 1h.

[0142] (3) Unloading and filtration operation: The reaction crystallizer is restored to normal pressure through the exhaust port and unloaded and filtered. At 38°C, the filter pump matched with the reaction crystallizer is turned on to perform solid-liquid separation. The filter cake is washed with deionized water and dried overnight (12.0h). The obtained yellowish-white flaky crystals are 2,6-NDC, with a yield of 95.0% and a purity of 99.9wt%. The filtrate contains 0.26wt% M,M-2,6-NDC.

[0143] Example 2 (Compared to Example 1, the upper limit of the reactant molar ratio is changed) This embodiment is basically the same as embodiment 1, except that: In step (1), 600g of crude 2,6-NDA (purity 95.0wt%), 4800g of anhydrous methanol and 60g of concentrated sulfuric acid (98.3wt% sulfuric acid) were added to the shell of the reaction crystallization vessel (the mass ratio of 2,6-NDA to anhydrous methanol was 1:8.0, the molar ratio was 1:54; the amount of concentrated sulfuric acid catalyst was 10%wt of 2,6-NDA).

[0144] In step (3), the yield of the yellowish-white flaky crystals 2,6-NDC was 93.5%, the purity was 99.93 wt%, and the filtrate contained 0.29 wt% M,M-2,6-NDC.

[0145] Example 3 (Compared to Example 1, the crystallization cooling rate parameter was changed) This embodiment is basically the same as embodiment 1, except that: In step (2), the temperature is reduced to 38.0℃ at a cooling rate of 15.0℃ / h.

[0146] In step (3), the yield of the yellowish-white flaky crystals 2,6-NDC was 95.2%, the purity was 99.8 wt%, and the filtrate contained 0.26 wt% M,M-2,6-NDC.

[0147] Example 4 (Compared with Example 1, the final crystallization temperature parameter was changed) This embodiment is basically the same as embodiment 1, except that: In step (2), the temperature is reduced to 28.0℃ at a rate of 10.0℃ / h and kept at 28℃ for 1h.

[0148] In step (3), the vacuum pump of the reaction crystallizer is turned on at 28°C; the yield of the yellowish-white flaky crystals 2,6-NDC is 95.6%, the purity is 99.75wt%, and the content of M,M-2,6-NDC in the filtrate is 0.24wt%.

[0149] Example 5 (Compared to Example 1, the reactant molar ratio was changed - lower limit) This embodiment is basically the same as embodiment 1, except that: In step (1), 600g of crude 2,6-NDA (purity 95.0wt%), 2400g of anhydrous methanol and 60g of concentrated sulfuric acid (98.3wt% sulfuric acid) were added to the shell of the reaction crystallization vessel (the mass ratio of 2,6-NDA to anhydrous methanol was 1:4.0, and the molar ratio was 1:27); the amount of concentrated sulfuric acid used as catalyst was 10%wt of 2,6-NDA).

[0150] In step (3), the yield of the yellowish-white flaky crystals 2,6-NDC was 69.5%, the purity was 89.7 wt%, and the filtrate contained 5.7 wt% M,M-2,6-NDC.

[0151] Example 6 (The initial crystallization temperature is different compared to Example 1) (1) Esterification reaction operation: 600g of crude 2,6-NDA (purity 95.0wt%), 3600g of anhydrous methanol and 60g of concentrated sulfuric acid (98.3wt% sulfuric acid) were added to the shell of the reaction crystallization vessel (the mass ratio of 2,6-NDA to methanol was 1:6.0, the molar ratio was 1:40.5; the amount of concentrated sulfuric acid catalyst was 10%wt of 2,6-NDA). The esterification reaction was carried out at 130℃, 1.0MPa (gauge pressure) and in air atmosphere for 5 hours. The steam generated during the esterification reaction was discharged from the reaction steam outlet and entered the storage tank of the adsorption and dehydration unit (containing 3A molecular sieve) through the reaction steam inlet. After adsorption and dehydration by the 3A molecular sieve in the storage tank at 50℃ for 4min (that is, the residence time of the reaction steam in the storage tank was 4min), it entered the condenser through the dehydration steam pipe and was condensed at 45℃ for 3min (that is, the residence time of the adsorbed and dehydrated steam in the condenser was 3min) to obtain the dehydrated methanol solution. The dehydrated methanol solution is continuously returned to the shell of the reaction crystallization vessel through the methanol reflux port. After the esterification reaction is completed, the adsorption dehydration unit is shut down to proceed with the crystallization operation.

[0152] (2) Crystallization operation: The reaction crystallizer begins to cool down. When the temperature of the solution inside the reaction crystallizer shell reaches 120℃, a slurry of 6g of 99.99wt% dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) and 76g of anhydrous methanol is pumped into the reaction crystallizer shell through the feed port. The temperature is then reduced to 38.0℃ at a rate of 10.0℃ / h using a programmed cooling method, and then kept at 38℃ for 1h.

[0153] (3) Unloading and filtration operation: The reaction crystallizer is restored to normal pressure through the exhaust port and unloaded and filtered. At 38°C, the filter pump matched with the reaction crystallizer is turned on to perform solid-liquid separation. The filter cake is washed with deionized water and dried overnight (12.0h). The obtained yellowish-white flaky crystals are 2,6-NDC, with a yield of 93.5% and a purity of 98.5wt%. The filtrate contains 0.36wt% M,M-2,6-NDC.

[0154] Comparative Example 1 (without introducing an adsorption dehydration unit compared to Example 1) The comparative method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization was carried out in the reaction crystallization vessel of Example 1, and specifically included the following steps: (1) Esterification reaction operation: 600g of crude 2,6-NDA (purity 95.0wt%), 3600g of anhydrous methanol and 60g of concentrated sulfuric acid (98.3wt% sulfuric acid) were added to the shell of the reaction crystallization vessel (the mass ratio of 2,6-NDA to anhydrous methanol was 1:6.0, the molar ratio was 1:40.5; the amount of concentrated sulfuric acid catalyst was 10%wt of 2,6-NDA). The esterification reaction was carried out at 130℃, 1.0MPa (gauge pressure) and in air atmosphere for 5 hours.

[0155] (2) Crystallization operation: The reaction crystallizer begins to cool down. When the temperature of the solution inside the reaction crystallizer shell reaches 128°C, a slurry consisting of 6g of 99.99wt% dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) and 76g of anhydrous methanol is pumped into the reaction crystallizer shell through the feed port. The temperature is then reduced to 38.0°C at a rate of 10.0°C / h using a programmed cooling method, and then held at 38°C for 1h.

[0156] (3) Unloading and filtration operation: The reaction crystallizer is restored to normal pressure through the exhaust port and unloading and filtration is performed. At 38°C, the filtration pump matched with the reaction crystallizer is turned on to perform solid-liquid separation. The filter cake is washed with deionized water and dried overnight (12.0h). The obtained yellowish-white flaky crystals are 2,6-NDC, with a yield of 90% and a purity of 98wt%. The filtrate contains 2.1wt% M,M-2,6-NDC.

[0157] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0158] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0159] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. An apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, characterized in that, include: A reaction crystallization vessel is used for the esterification reaction of crude 2,6-naphthalenedicarboxylic acid with methanol to produce dimethyl 2,6-naphthalenedicarboxylic acid and crystallize it; the reaction crystallization vessel has a methanol reflux port, a reaction vapor outlet, a discharge port and an exhaust port; An adsorption dehydration unit includes a storage tank and a condenser. The outer surface of the storage tank is provided with a first jacket. The storage tank contains a dehydrating agent and has a dehydration steam outlet and a reaction steam inlet. A dehydration steam pipe is installed in the dehydration steam outlet. The lower end of the dehydration steam pipe extends to a position near the bottom of the storage tank. The upper end of the dehydration steam pipe is connected to the condenser and the methanol reflux port in sequence. The reaction steam inlet is connected to the reaction steam outlet.

2. The apparatus according to claim 1, characterized in that, The reaction crystallization vessel includes: The housing has the methanol reflux port, the reaction vapor outlet, the discharge port and the exhaust port, and the outer surface of the housing is provided with a second jacket; A refrigerant inlet and a refrigerant outlet are provided. A stirrer is mounted on the housing and includes a motor, a rotating shaft, and a first stirring blade located inside the guide tube.

3. The apparatus according to claim 2, characterized in that, Both the second jacket and the guide tube are provided with at least one guide plate inside; And / or, the guide tube is located below the cooling crystallization liquid level; And / or, the first impeller is a four-bladed propulsion impeller; And / or, the stirrer further includes a second stirring blade; the second stirring blade is located below the first stirring blade and extends partially below the guide tube; the second stirring blade is a rake-type stirring blade and has multiple through holes in at least a portion of its area; And / or, the bottom of the housing is provided with the discharge port, and a discharge valve is installed at the discharge port. The discharge valve includes a downward-expanding discharge valve and a ball valve, and the ball valve is connected in series below the downward-expanding discharge valve.

4. The apparatus according to claim 1, characterized in that, The dehydrating agent is filled into the storage tank; And / or, the dehydrating agent includes at least one of molecular sieve dehydrating agent, silica gel, and anhydrous calcium chloride, preferably 3A molecular sieve; And / or, the size of the dehydrating agent is larger than the size of the air inlet of the dehydrating steam pipe, and the size of the dehydrating agent is larger than the size of the reaction steam inlet; And / or, a temperature sensor is installed on the reaction crystallization vessel; And / or, the purity of the crude 2,6-naphthalenedicarboxylic acid is 92-95 wt%; And / or, the apparatus for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes a filtration unit connected to the discharge port; Preferably, the filtration unit is a vacuum pump.

5. A method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization, applied to the apparatus as described in any one of claims 1 to 4, characterized in that, include: The crude 2,6-naphthalenedicarboxylic acid and methanol were subjected to an esterification reaction in the reaction crystallization vessel under the action of a catalyst; The vapor from the esterification reaction process enters the adsorption and dehydration unit for dehydration and condensation to obtain a dehydrated methanol solution. The dehydrated methanol solution is continuously returned to the reaction crystallization vessel; After the esterification reaction is completed, the adsorption and dehydration unit is turned off, and the product of the esterification reaction is cooled and crystallized.

6. The method according to claim 5, characterized in that, The cooling crystallization includes the following steps: (1) The product of the esterification reaction is subjected to a first cooling; (2) After the first cooling, dimethyl 2,6-naphthalenedicarboxylate and methanol with a purity of more than 99 wt% are added, followed by a second cooling and heat preservation.

7. The method according to claim 6, characterized in that, The termination temperature of the first cooling is 120-136℃; And / or, in step (2), the mass ratio of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher to the methanol is 6:(70-82), and the amount of the dimethyl 2,6-naphthalenedicarboxylate with a purity of 99 wt% or higher is 0.5-1.5% of the mass of the crude 2,6-naphthalenedicarboxylate; And / or, the second cooling method is programmed cooling; And / or, the cooling rate of the second cooling is 8-15℃ / h; And / or, the termination temperature of the second cooling is 28-46°C; And / or, the heat preservation time is 0.5-1.5h.

8. The method according to claim 5, characterized in that, The reaction temperature for the esterification reaction is 120-140℃; And / or, the reaction pressure of the esterification reaction is 0.8-1.2 MPa; And / or, the reaction time of the esterification reaction is 4-6 hours; And / or, the molar ratio of the crude 2,6-naphthalenedicarboxylic acid to methanol participating in the esterification reaction is 1:(27-54). And / or, the catalyst comprises concentrated sulfuric acid.

9. The method according to claim 5, characterized in that, The condensation temperature is 35-55℃; And / or, the dehydration temperature is 40-60°C.

10. The method according to claim 5, characterized in that, The method for preparing dimethyl 2,6-naphthalenedicarboxylate by reaction crystallization further includes: After the cooling and crystallization, the reaction crystallization vessel is restored to normal pressure, and then unloaded, filtered, washed, and dried.

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