Method and system for producing dimethyl naphthalate

Abstract

The invention discloses a method and a system for producing dimethyl naphthalate. The method sequentially comprises the steps of oxidation, deep oxidation, oxidation crystallization, oxidation filtration, esterification, purification, esterification filtration, drying and the like. When dimethyl naphthalate is prepared, through two-stage esterification, the reaction process can be controlled, the conversion per pass can be improved, the content of intermediate products such as monoester can be reduced, and reaction products can be separated more easily; meanwhile, the novel catalyst system can reduce corrosion to equipment. The implementation of the whole process has operability, and the operation cost is relatively low; and secondly, through a combined process of rectification, recrystallization and one-step rotary pressure filtration, impurities can be effectively removed, the chromaticity of the product is improved, and then the dimethyl naphthalate product with the purity not lower than 99.5% is obtained.

Description

Technical Field

[0001] The present invention relates to a method and system for producing dimethyl naphthalene dicarboxylate. Background Art

[0002] Dimethyl naphthalate (NDC) is a very important chemical product. It is a key monomer in the production of polyethylene naphthalate (PEN). The end product PEN is widely used in many fields such as membrane materials, flexible printed circuit boards (FPC), fuel cell seals, electrical heat-resistant insulation, speaker membranes, food-grade pharmaceutical packaging, aerospace materials, etc.

[0003] At present, dimethyl naphthalene dicarboxylate (NDC) is produced in two stages in industry. Dimethyl naphthalene (DMN) is used as raw material. In the presence of cobalt, manganese and bromine, acetic acid is used as solvent to generate naphthalene dicarboxylic acid (NDA) through oxidation reaction. Then, crude naphthalene dicarboxylic acid is obtained through crystallization, filtration and drying. The crude naphthalene dicarboxylic acid is then esterified with methanol under the catalysis of sulfuric acid to obtain dimethyl naphthalene dicarboxylate. Summary of the invention

[0004] In order to increase the process selection routes for dimethyl naphthalate, the embodiments of the present invention provide a system and method for producing dimethyl naphthalate with strong operability, high product purity and low cost.

[0005] As one aspect of the present invention, it relates to a method for producing dimethyl naphthalene dicarboxylate, the method comprising:

[0006] In an oxidation reactor, dialkylnaphthalene, catalyst I and solvent are oxidized with oxygen-containing gas under a first oxidation condition to obtain oxidation slurry I;

[0007] In a deep oxidation reactor, the oxidized slurry I is deeply oxidized under a second oxidation condition to obtain an oxidized slurry II;

[0008] In an oxidation crystallization device, the oxidation slurry II is crystallized under a first crystallization condition to obtain oxidation slurry III;

[0009] In an oxidation pressure filter, filtering and washing the oxidation slurry III to obtain an oxidation filter cake;

[0010] In the esterification slurry preparation device, the oxidation filter cake and the esterification circulating solvent are prepared into esterification slurry I according to the mass ratio of the naphthalene dicarboxylic acid and the methanol;

[0011] In an esterification slurry heating device, the esterification slurry I is heated to obtain esterification slurry II;

[0012] In a first esterification reactor, the esterification slurry II, methanol and catalyst II are esterified under the first esterification conditions to obtain an esterification product I;

[0013] In a second esterification reactor, the esterification product I is re-esterified under a second esterification condition to obtain an esterification product II;

[0014] In the esterification purification device, the esterification product II is purified to obtain an esterification product slurry;

[0015] In an esterification filtration device, the esterification product slurry is filtered, washed and dehumidified to obtain an esterification filter cake;

[0016] In a drying device, the esterification filter cake is dried to obtain dimethyl naphthalate product.

[0017] In one or some possible embodiments, filtering and washing the oxidation slurry III in an oxidation pressure filter to obtain an oxidation filter cake comprises:

[0018] In the oxidation pressure filter, the oxidation slurry III passes through the filtration zone and multi-stage washing zone of the oxidation pressure filter in sequence to obtain an oxidation filter cake and a filtrate;

[0019] After the filtrate is treated by the separation unit, a mother liquor, a washing liquid and a waste liquid are obtained; the mother liquor and the washing liquid are circulated to the oxidation reactor for repeated utilization, and the waste liquid is discharged for sewage treatment.

[0020] In one or some possible embodiments, in the esterification purification device, purifying the esterification product II to obtain an esterification product slurry includes:

[0021] In the esterification distillation device, the esterification product II is separated into light and heavy components to obtain light components, products, and heavy components; the light components and products are then recrystallized in a recrystallization device to obtain an esterification product slurry;

[0022] Alternatively, the esterification product II is recrystallized in a recrystallization device to obtain a recrystallized esterification product II; the recrystallized esterification product II is then distilled in an esterification distillation device to remove light and heavy components to obtain an esterification product slurry.

[0023] In one or some possible embodiments, in the recrystallization device, the recrystallization solvent is methanol; and the mass ratio of the methanol to the esterification product II is 3:1 to 20:1.

[0024] In one or some possible embodiments, in the oxidation reactor, dialkylnaphthalene, catalyst I and solvent are oxidized with oxygen-containing gas under first oxidation conditions to obtain oxidation slurry I, comprising:

[0025] The catalyst I is selected from a catalyst system containing cobalt, manganese, and bromine or a ligand structure catalyst system formed by cobalt and one or more metals selected from vanadium, molybdenum, nickel, and tungsten, and the cobalt ion concentration is 300ppm to 1500ppm;

[0026] The mass ratio of the solvent to the dialkylnaphthalene is 3:1 to 20:1;

[0027] The solvent is selected from a mixture of C2-C6 monocarboxylic acid and water, wherein the water content is 5-20 wt%;

[0028] The first oxidation conditions are: oxidation temperature of 160-205°C, pressure of 0.7-3MPaG, and residence time of 30-90min;

[0029] The oxygen-containing gas is selected from one of air, oxygen, oxygen-deficient gas or oxygen-enriched gas.

[0030] In one or some possible embodiments, the second oxidation condition is: oxidation temperature is 190-250° C., pressure is 1.0-4.0 MPaG, and residence time is 30-150 min.

[0031] In one or some possible embodiments, the first crystallization condition is: crystallization pressure -0.05 to 0.1 MPaG.

[0032] In one or some possible embodiments, the mass ratio of the naphthalene dicarboxylic acid to the methanol is 3:1 to 20:1.

[0033] In one or some possible embodiments, in the first esterification reactor, the esterification slurry II, methanol and catalyst II are esterified under the first esterification conditions to obtain the esterification product I, comprising:

[0034] The catalyst II is selected from one or more of benzenesulfonic acid, tetrabutyl titanate, tributyl phosphate, imidazole or pyridine acidic ionic liquids;

[0035] The first esterification conditions are: esterification temperature 170-280° C., time 1-4 h.

[0036] In one or some possible embodiments, the second esterification conditions are: esterification temperature 150-210° C., time 1-4 h.

[0037] In one or some possible embodiments, the moisture content of the esterification filter cake is 5-15%.

[0038] As another aspect of the present invention, it relates to a system for producing dimethyl naphthalate, which is used to implement the above method, comprising: an oxidation reactor, a deep oxidation reactor, an oxidation crystallization device, an oxidation pressure filter, an esterification slurry preparation device, an esterification slurry heating device, a first esterification reactor, a second esterification reactor, an esterification purification device, an esterification filtering device and a drying device;

[0039] The oxidation reactor is connected to the deep oxidation reactor and is used to deeply oxidize the incompletely oxidized dialkylnaphthalene and the intermediate products in the oxidation slurry I to obtain the oxidation slurry II;

[0040] The deep oxidation reactor is connected to the oxidation crystallization device, and the oxidation crystallization device is connected to the oxidation pressure filter, which is used to filter and wash the oxidation slurry III to obtain the oxidation filter cake;

[0041] The oxidation pressure filter is connected to the esterification slurry preparation device, and is used to prepare the oxidation filter cake into the esterification slurry I according to a set mass ratio;

[0042] The esterification slurry preparation device is connected to the esterification slurry heating device and is used to preheat the esterification slurry I;

[0043] The esterification slurry heating device is connected to the first esterification reactor, and the first esterification reactor is connected to the second esterification reactor, and is used for secondary esterification of the monoester by-product contained in the esterification product I to generate the esterification product II;

[0044] The second esterification reactor is connected to the esterification purification device to purify the esterification product II to obtain the esterification product slurry;

[0045] The esterification purification device is connected to the esterification filtration device and is used for filtering, washing and dehumidifying to obtain an esterification filter cake;

[0046] The esterification filtering device is connected to the drying device and is used to dry the esterification filter cake to obtain a dimethyl naphthalate product.

[0047] In one or some possible embodiments, the esterification purification device includes an esterification distillation device and a recrystallization device;

[0048] The esterification distillation device is used to separate the light and heavy components in the esterification product II;

[0049] The recrystallization device is used to remove light components and some impurities contained in the esterification product II.

[0050] The beneficial effects of the above technical solution provided by the embodiment of the present application include at least:

[0051] (1) In the preparation of naphthalenedicarboxylic acid, the present invention uses a novel catalyst to oxidize dimethylnaphthalene, and in combination with the production method adopted by the present invention, not only the reaction depth is effectively controlled, and the product loss caused by overoxidation is reduced; at the same time, the product yield can be improved and the purity of the product can be ensured through deep oxidation, thereby reducing the content of impurities in the oxidation product, and providing a high-quality intermediate product for the subsequent process flow.

[0052] (2) The present invention uses a rotary pressure filter in the production process to achieve the slurry filtering, washing and dehumidification process, which not only shortens the process flow and reduces energy consumption, but also reduces investment and land occupation, and can achieve better economic benefits.

[0053] (3) The present invention can control the reaction process, improve the single-pass conversion rate, reduce the content of intermediate products such as monoester, and make the reaction product easier to separate through two-stage esterification when preparing dimethyl naphthalate; at the same time, the new catalyst system can reduce the corrosion to the equipment. The implementation of the overall process is operable and has a low operating cost.

[0054] (4) The present invention can effectively remove impurities and improve product color through the combined process of distillation + recrystallization + one-step rotary pressure filtration, thereby obtaining a dimethyl naphthalate product with a purity of not less than 99.5%.

[0055] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0057] Figure 1 The process flow chart of producing dimethyl naphthalate of the present invention is as follows:

[0058] In the figure: 101, oxidation reactor; 102, deep oxidation reactor; 103, oxidation crystallization device; 104, oxidation pressure filter; 105, esterification slurry preparation device; 106, esterification slurry heating device; 107, first esterification reactor; 108, second esterification reactor; 109, esterification purification device; 110, esterification distillation device; 111, recrystallization device; 112, esterification filtering device; 113, drying device; 114, oxidation solvent separation unit; 115, esterification solvent separation unit; 116, steam generator; 117, gas-liquid separator; 118, circulating water cooler; 119, tail gas separation tower; 120 dehydration tower;

[0059] a, oxygen-containing gas; b, dialkylnaphthalene; c, catalyst I and solvent; d, oxidation slurry I; e, oxidation slurry II; f, oxidation slurry III; g, oxidation filter cake; h, esterification slurry I; i, esterification slurry II; j, esterification product I; k, esterification product II; l, esterification product slurry; m, esterification filter cake; n, dimethyl naphthalene dicarboxylate product; o, esterification circulating solvent; p, methanol and catalyst II. DETAILED DESCRIPTION

[0060] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0061] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0062] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0063] In the description of the present invention, it should be noted that the terms "include", "including", "have", "contain" and the like are open terms, meaning including but not limited to.

[0064] When the inventors explored the production method of dimethyl naphthalene dicarboxylate, they found that the existing production technology of naphthalene dicarboxylic acid (NDA) and dimethyl naphthalene dicarboxylate (NDC) mainly had the following four problems:

[0065] (1) Low oxidation reaction yield and difficult separation. When the oxidation reaction of dimethylnaphthalene is not sufficient, more intermediate aldehydes and naphthalene monocarboxylic acid products will be produced, resulting in a lower product yield; when dimethylnaphthalene undergoes an overoxidation reaction, more impurities will be generated, such as trimellitic acid and naphthoic acid, among which the content of trimellitic acid can be as high as 5%, which not only affects the product yield, but also makes the separation of the product more difficult.

[0066] (2) Filtration and separation operations are complex and energy consumption is high. The separation of oxidation slurry and esterification slurry generally adopts centrifugal separation or vacuum separation. If centrifugal separation is selected, not only will the separation operation be complicated and the mechanical failure rate be high; but also due to the poor operating environment, the process operation energy consumption will increase and the amount of waste liquid discharged will increase; if vacuum separation is selected, it needs to be carried out in a vacuum environment, and its energy consumption is also relatively high. In the actual operation process, the power consumption of these two methods is as high as 15kWh / t, and the steam consumption per ton of product is 0.1-0.2t when the filtered cake is dried.

[0067] (3) Low conversion rate and yield of esterification per pass. The conversion rate of the esterification process per pass is low. The conversion rate of the first-stage esterification can generally only reach 88-90%, which affects the product yield. Therefore, only partial reflux of the product can be used for cyclic esterification. In addition, the use of acidic catalysts in the esterification step will not only seriously corrode the equipment, but also increase the esterification temperature and subsequent distillation temperature. In the actual process operation, the vacuum needs to reach nearly 300°C, and the corrosion of sulfuric acid and other substances to the equipment is difficult to avoid.

[0068] (4) Product purification is difficult. The impurities of esterification products are complex, including monoesters and polycyclic substances. Impurities formed during the oxidation process will also esterify to form trimellitic acid esters, naphthoic acid esters, etc. These substances are difficult to completely remove by simple distillation or recrystallization. In addition, trace substances that affect color are also difficult to remove by simple separation, which directly affects the key indicators of subsequent polymerization products such as degree of polymerization, stability and color.

[0069] In summary, although there have been some studies on the production technology of NDA and NDC, there are still problems in the whole process, such as difficult oxidation reaction control, many impurities, complex separation, serious corrosion of esterification catalysts, difficulty in product purification, and impurities affecting the color of the end product. Therefore, it is necessary to find a better process solution to improve the yield, reduce consumption, reduce pollutant emissions, mild reaction conditions, and efficient catalysts, etc., to promote clean production and energy saving and consumption reduction.

[0070] In view of the fact that the prior art cannot meet the inventor's expectations, the inventor made the present invention after further research and development.

[0071] See attached Figure 1The method and system for producing dimethyl naphthalate product n of the present invention are further described:

[0072] (1) In an oxidation reactor 101, dialkylnaphthalene b, catalyst I and solvent c are introduced into the reactor and react with oxygen in oxygen-containing gas a under a first oxidation condition to obtain an oxidation slurry Id;

[0073] (2) introducing the oxidized slurry Id into a deep oxidation reactor 102 for deep oxidation, and further oxidizing the incompletely oxidized dialkylnaphthalene b and the intermediate products aldehyde and monocarboxylic acid to obtain an oxidized slurry IIe;

[0074] (3) passing the oxidized slurry IIe into an oxidized crystallization device 103, and crystallizing under the first crystallization condition to obtain an oxidized slurry IIIf;

[0075] (4) The oxidation slurry IIIf is passed into the oxidation pressure filter 104 for filtration and washing to obtain an oxidation filter cake g; after the filtrate is treated by the oxidation solvent separation unit 114, most of the mother liquor and washing liquid are returned to the oxidation reaction system for recycling, and a small amount of waste liquid 206 is discharged to sewage treatment;

[0076] (5) the oxidation filter cake g is introduced into the esterification slurry preparation device 105 and prepared with the esterification circulating solvent o into the esterification slurry Ih;

[0077] (6) passing the esterified slurry Ih into the esterified slurry heating device 106 for heating to obtain the esterified slurry IIk;

[0078] (7) introducing the esterification slurry IIk, methanol and catalyst IIp into the first esterification reactor 107, and performing esterification under the first esterification conditions to obtain an esterification product Ij;

[0079] (8) The esterification product Ij is introduced into a second esterification reactor 108 under a second esterification condition for further esterification to obtain an esterification product IIk;

[0080] (9) The esterification product IIk is sequentially introduced into an esterification distillation device 110 and a recrystallization device 111 for purification to obtain an esterification product slurry 1;

[0081] (10) passing the esterification product slurry l into the esterification filtration device 112 for filtration, washing and dehumidification to obtain an esterification filter cake m;

[0082] (11) The esterification filter cake m is passed into a drying device 113 for drying to obtain dimethyl naphthalene dicarboxylate product n.

[0083] (12) The tail gas generated after the first oxidation in the oxidation reactor 101 is sent to the steam generator 116 connected in series to generate steam to recover energy; the steam is then sent to the gas-liquid separator 117 for condensation, and the condensed liquid phase is returned to the deep oxidation reactor 102. The gas is further cooled by the circulating water cooler 118, and then the obtained gas enters the tail gas separation tower 119 for emission in compliance with the standards; the oxidizing solvent in the oxidation reactor 101 and / or the deep oxidation reactor 102 is sent to the dehydration tower 120 for dehydration, and the obtained concentrated acid is returned to the oxidation reactor and / or the deep oxidation reactor 102 for recycling, and the wastewater containing trace amounts of acid is discharged for sewage treatment.

[0084] The present invention is further described below in conjunction with specific examples, and the protection scope of the present invention is not limited by the following examples. The sources of materials mainly involved in the examples are all conventional commercial products.

[0085] Embodiment 1

[0086] The embodiment of the present invention provides a method for producing dimethyl naphthalate, the method comprising:

[0087] In the oxidation reactor 101, dialkylnaphthalene b, catalyst I and solvent c are oxidized with oxygen-containing gas a under the first oxidation condition to obtain oxidation slurry Id;

[0088] In the embodiment of the present invention, the catalyst I is selected from a catalyst system containing cobalt, manganese, and bromine or a ligand structure catalyst system formed by cobalt and one or more metals selected from vanadium, molybdenum, nickel, and tungsten, and the cobalt ion concentration is 300ppm to 1500ppm;

[0089] In a specific embodiment, the catalyst I used in the present invention is preferably selected from a catalyst system containing cobalt, manganese and bromine, and the concentration of the cobalt ion is 300 ppm to 1500 ppm.

[0090] In an embodiment of the present invention, the mass ratio of the solvent to the dialkylnaphthalene b is 3:1 to 20:1; the solvent is selected from a mixture of C2 to C6 monocarboxylic acids and water, and the content of water is 5 to 20 wt%;

[0091] In a specific embodiment, the preferred mass ratio of the solvent to the dialkylnaphthalene b is 5:1 to 10:1; the solvent is preferably a mixture of acetic acid and water, and the mass content of water is 7 to 20 wt%.

[0092] In the embodiment of the present invention, the first oxidation condition is: oxidation temperature is 160-205° C., pressure is 0.7-3 MPaG, and residence time is 30-90 min;

[0093] In a specific embodiment, the first oxidation condition is preferably: oxidation temperature is 180-195° C., pressure is 1.5-2.0 MPaG, and residence time is 45-60 min.

[0094] In an embodiment of the present invention, the oxygen-containing gas a is selected from one of air, oxygen, oxygen-deficient gas or oxygen-rich gas.

[0095] In a specific embodiment, the oxygen-containing gas a of the present invention is preferably air.

[0096] In the deep oxidation reactor 102, the oxidized slurry Id is deeply oxidized under the second oxidation condition to obtain an oxidized slurry IIe;

[0097] In an embodiment of the present invention, the second oxidation conditions are: oxidation temperature of 190-250° C., pressure of 1.0-4.0 MPaG, and residence time of 30-150 min;

[0098] In a specific embodiment, the second oxidation condition is preferably: oxidation temperature is 200-220° C., pressure is 1.8-2.2 MPaG, and residence time is 75-120 min.

[0099] In the embodiment of the present invention, the oxygen in the deep oxidation reactor 102 comes from the tail gas generated after the first oxidation in the oxidation reactor 101, which is generally an oxygen-depleted gas. In the tail gas, the mass content of oxygen is generally 3.5wt%.

[0100] In an embodiment of the present invention, the tail gas generated after the first oxidation in the oxidation reactor 101 is sent to the steam generator 116 in series to generate steam to recover energy; the steam is then sent to the gas-liquid separator 117 for condensation, and the condensed liquid phase is returned to the deep oxidation reactor 102. The gas is further cooled by the circulating water cooler 118, and the obtained gas enters the tail gas separation tower 119 for meeting the emission standards, including: in the process of tail gas treatment, it is sprayed with acid solution and desalted water, and then catalytically oxidized for meeting the emission standards.

[0101] In an embodiment of the present invention, the oxidizing solvent in the oxidation reactor 101 and / or the deep oxidation reactor 102 is sent to the dehydration tower 120 for dehydration, and the concentrated acid obtained is returned to the oxidation reactor 101 and / or the deep oxidation reactor 102 for recycling, and the wastewater containing trace amounts of acid is discharged for sewage treatment.

[0102] In the oxidation crystallization device 103, the oxidation slurry IIe is crystallized under the first crystallization condition to obtain oxidation slurry IIIf;

[0103] In the embodiment of the present invention, the oxidation slurry IIe is subjected to pressure reduction crystallization in the oxidation crystallization device 103 to obtain the oxidation slurry IIIf, wherein the first crystallization condition is -0.05 to 0.1 MPaG;

[0104] In a specific embodiment, the first crystallization condition is -0.02 to 0.05 MPaG.

[0105] In the oxidation pressure filter 104, the oxidation slurry IIIf is filtered and washed to obtain an oxidation filter cake g;

[0106] In the embodiment of the present invention, the oxidation pressure filter 104 is a rotary pressure filter, which is divided into a filtering area and a multi-stage washing area; the washing liquid enters from the last-stage washing area, and the last-stage washing liquid is used as the washing liquid of the previous stage, and finally discharged from the first-stage washing area; wherein the washing liquid is a mixture of methanol and water in any mass ratio;

[0107] In a specific embodiment, the washing liquid is preferably a mixture of methanol and water, and the preferred mass ratio is 95:5 to 99:1.

[0108] In the embodiment of the present invention, the oxidation slurry IIIf passes through the filtration zone and the multi-stage washing zone of the oxidation pressure filter 104 in sequence to obtain an oxidation filter cake g and a filtrate;

[0109] The filtrate is treated by the oxidation solvent separation unit 114 to obtain a mother liquor, a washing liquid and a waste liquor; the mother liquor and the washing liquid are circulated to the oxidation reactor 101 for repeated use, and the waste liquor is discharged for sewage treatment.

[0110] In the embodiment of the present invention, the oxidation filter cake g is directly fed into the esterification slurry preparation device 105. In the oxidation filter cake g, the residual content of acetic acid in the liquid phase of the oxidation filter cake g is 0.1-3%, preferably 1-2%.

[0111] In an embodiment of the present invention, the filtrate is treated by an oxidizing solvent separation unit 114 to obtain a mother liquor, a washing liquid and a waste liquor; wherein the mother liquor contains a certain amount of water and an acetic acid solution containing impurities; the washing liquid contains a methanol solution containing acetic acid and water; and the waste liquor contains water and an acetic acid solution containing impurities (extracted in a certain proportion of the mother liquor).

[0112] In a specific embodiment, the mother liquor and washing liquid are recycled in the return device oxidation reaction system, and the waste liquid is discharged to sewage treatment.

[0113] In the esterification slurry preparation device 105, the oxidation filter cake g and the esterification circulating solvent o are prepared into the esterification slurry Ih according to the mass ratio of the naphthalene dicarboxylic acid and the methanol; wherein the esterification circulating solvent o is methanol.

[0114] In an embodiment of the present invention, the mass ratio of the naphthalene dicarboxylic acid to the methanol is 3:1 to 20:1;

[0115] In a specific embodiment, the preferred mass ratio of the naphthalene dicarboxylic acid to the methanol is 5:1 to 10:1.

[0116] In the esterification slurry heating device 106, the esterification slurry Ih is heated to obtain the esterification slurry IIi;

[0117] In the embodiment of the present invention, the purpose of heating the esterification slurry Ih is to dissolve naphthalene dicarboxylic acid in methanol to form a homogeneous reaction system.

[0118] In the first esterification reactor 107, the esterification slurry IIi, methanol and catalyst IIp are esterified under the first esterification conditions to obtain an esterification product Ij;

[0119] In an embodiment of the present invention, the catalyst II is selected from one or more of benzenesulfonic acid, tetrabutyl titanate, tributyl phosphate, imidazole or pyridine acidic ionic liquids;

[0120] In a specific embodiment, the catalyst II is preferably a mixture of tetrabutyl titanate and tributyl phosphate in any ratio.

[0121] In the embodiment of the present invention, the first esterification conditions are: esterification temperature 170-280° C., time 1-4 h.

[0122] In a specific embodiment, the first esterification conditions are: esterification temperature 180-210° C., time 2-3 h.

[0123] In the embodiment of the present invention, the esterification slurry II and methanol are esterified and dehydrated under the action of the catalyst II to obtain the esterification product I.

[0124] In the second esterification reactor 108, the esterification product Ij is re-esterified under the second esterification conditions to obtain the esterification product IIk;

[0125] In the embodiment of the present invention, the esterification product Ij enters the second esterification reactor 108 for re-esterification, part of the solvent and water generated by the reaction are discharged from the top of the second esterification reactor 108, and the esterification product IIk enters the extraction process.

[0126] In the embodiment of the present invention, the second esterification conditions are: esterification temperature 150-210° C., time 1-4 h.

[0127] In a specific embodiment, the second esterification conditions are preferably: esterification temperature 185-205° C., time 2-3 h.

[0128] In the esterification purification device 109, the esterification product IIk is purified to obtain an esterification product slurry l;

[0129] In the embodiment of the present invention, the esterification product IIk may be first distilled and then recrystallized, or first recrystallized and then distilled.

[0130] In a specific embodiment, in the esterification purification device 109, the esterification product IIk is purified to obtain the esterification product slurry l, comprising:

[0131] In the esterification distillation device 110, the esterification product IIk is separated into light and heavy components to obtain light components, products and heavy components; wherein the light components and products are discharged from the top of the tower, and the heavy components are discharged from the bottom of the tower; the light components and products are then recrystallized in the recrystallization device 111 to remove the light components and some impurities in the product to obtain an esterification product slurry.

[0132] In a specific embodiment, in the esterification purification device 110, the esterification product IIk is purified to obtain the esterification product slurry l, comprising:

[0133] In the recrystallization device 111, the esterification product IIk is recrystallized to remove some light components and impurities in the esterification product IIk to obtain an esterification product IIk containing heavy components; then the esterification product IIk containing heavy components is distilled in the esterification distillation device 110 to remove light and heavy components to obtain an esterification product slurry l.

[0134] In an embodiment of the present invention, the light components include but are not limited to methanol, methyl acetate, dimethyl ether, etc., the impurities include but are not limited to trimellitic acid and its esters, unreacted naphthalene dicarboxylic acid, etc., and the heavy components include but are not limited to anthracene substances with three benzene rings, tars, etc., which are discharged from the bottom of the tower.

[0135] In the embodiment of the present invention, in the recrystallization device 111, the recrystallization solvent is preferably methanol; the mass ratio of the methanol to the esterification product II is 3:1 to 20:1.

[0136] In a specific embodiment, the impurities, light components and heavy components removed during the second esterification reaction and distillation process are processed by the esterification solvent separation unit 115, and the methanol is recycled and used, and the wastewater containing impurities is discharged for sewage treatment.

[0137] In the esterification filtration device 112, the esterification product slurry l is filtered, washed and dehumidified to obtain an esterification filter cake m;

[0138] In the embodiment of the present invention, the esterification product slurry 1 is filtered, washed and dehumidified by an esterification filtration device 112; the esterification filtration device 112 can be a two-stage centrifuge or a rotary pressure filter, and the esterification filtration device of the present invention is preferably a rotary pressure filter.

[0139] In a specific embodiment, the esterification rotary pressure filter is divided into a filtration zone, a multi-stage washing zone and a dehumidification zone. The washing liquid enters from the last washing zone, and the last washing liquid is used as the washing liquid of the previous stage, and finally discharged from the first washing zone.

[0140] In the embodiment of the present invention, the washing liquid is a mixture of methanol and water in any mass ratio. The present invention preferably uses a mixture of methanol and water, and the preferred mass ratio is 95:5 to 99:1.

[0141] In the embodiment of the present invention, the dehumidification zone is used to further remove the solvent, and the moisture content is 3 to 12%, and preferably 5 to 8% in the present invention.

[0142] In a specific embodiment, the mother liquor and washing liquid produced in the esterification rotary pressure filter are processed by the esterification solvent separation unit 115 and recycled for reuse.

[0143] In the drying device 113, the esterification filter cake m is dried to obtain dimethyl naphthalene dicarboxylate product n.

[0144] In a specific embodiment, the solvent removed in the drying device 113 is processed by the esterification solvent separation unit 115, and the methanol is recovered and recycled.

[0145] In the embodiment of the present invention, the esterification filter cake m is dried to obtain dimethyl naphthalene dicarboxylate product n, and the purity of the product is not less than 99%, and can reach up to 99.8%.

[0146] Embodiment 2

[0147] Based on the same inventive concept, this embodiment provides a system for producing dimethyl naphthalate by implementing the above method, comprising: an oxidation reactor 101, a deep oxidation reactor 102, an oxidation crystallization device 103, an oxidation pressure filter 104, an esterification slurry preparation device 105, an esterification slurry heating device 106, a first esterification reactor 107, a second esterification reactor 108, an esterification purification device 109, an esterification filtering device 112 and a drying device 113;

[0148] The oxidation reactor 101 is connected to the deep oxidation reactor 102, and is used to deeply oxidize the incompletely oxidized dialkylnaphthalene and the intermediate products in the oxidation slurry Id to obtain the oxidation slurry IIe;

[0149] The deep oxidation reactor 102 is connected to the oxidation crystallization device 103, and the oxidation crystallization device 103 is connected to the oxidation pressure filter 104, which is used to filter and wash the oxidation slurry IIIf to obtain the oxidation filter cake g;

[0150] The oxidation pressure filter 104 is connected to the esterification slurry preparation device 105, and is used to prepare the oxidation filter cake g into the esterification slurry Ih according to a set mass ratio;

[0151] The esterification slurry preparation device 105 is connected to the esterification slurry heating device 106 and is used to preheat the esterification slurry for Ⅰh;

[0152] The esterification slurry heating device 106 is connected to the first esterification reactor 107, and the first esterification reactor 107 is connected to the second esterification reactor 108, and is used for secondary esterification of the monoester by-product contained in the esterification product Ih, such as monomethyl naphthalene dicarboxylate, to generate the esterification product IIi;

[0153] The second esterification reactor 108 is connected to the esterification purification device 109 to purify the esterification product IIk to obtain the esterification product slurry l;

[0154] The esterification purification device 109 is connected to the esterification filtration device 112 and is used for filtering, washing and dehumidifying to obtain an esterification filter cake m;

[0155] The esterification filtration device 112 is connected to the drying device 133 and is used to dry the esterification filter cake m to obtain dimethyl naphthalene dicarboxylate product n.

[0156] In the embodiment of the present invention, the deep oxidation reactor 102 may be one or multiple reactors connected in series.

[0157] In the embodiment of the present invention, the oxidation crystallization device 103 may be one unit or multiple units connected in series.

[0158] In the embodiment of the present invention, the esterification purification device 109 includes an esterification distillation device 110 and a recrystallization device 111;

[0159] The esterification distillation device 110 is used to separate the light and heavy components in the esterification product IIk;

[0160] The recrystallization device 111 is used to remove light components and some impurities contained in the esterification product IIk.

[0161] In the embodiment of the present invention, at least one esterification distillation device 110 is provided, and a plurality of esterification distillation devices 110 are arranged in series.

[0162] Embodiment 3

[0163] Combined with Figure 1 In the oxidation reactor 101, acetic acid and water are used as solvents, and under the action of cobalt, manganese and bromine catalysts, the raw material 2,6-dimethylnaphthalene (2,6-DMN) reacts with air to generate oxidation slurry Id - naphthalene dicarboxylic acid;

[0164] The feed flow rate of 2,6-DMN was controlled to be 1135 kg / h, the mass ratio of the solvent to the dialkylnaphthalene was 10:1, the mass content of water in the solvent was 8%, cobalt: manganese: bromine = 1:1:2, and the cobalt ion concentration was 800 ppm. The reaction operating temperature was 190° C., the operating pressure was 1.7 MPaG, and the reaction residence time was 45 min.

[0165] The oxidation slurry Id is introduced into the first deep oxidation reactor 102 for further deep oxidation. The oxygen-containing gas a is the tail gas after the oxidation reaction is completed, wherein the oxygen content is 3.5%. The deep oxidation reaction operating temperature is 220°C, the operating pressure is 2.2 MPaG, and the reaction residence time is 45 minutes.

[0166] After the reaction is completed, it enters the second deep oxidation reactor 102 to continue the reaction. The oxygen-containing gas a is the tail gas discharged from the first deep oxidation reactor 102, in which the oxygen content is 0.5%. The reaction conditions are an operating temperature of 200°C, an operating pressure of 1.8 MPaG, and a reaction residence time of 45 minutes to obtain an oxidized slurry IIe.

[0167] The oxidation slurry IIe is sequentially fed into the oxidation crystallization device 103, the pressure of the first crystallizer is controlled at 0.24 MPaG, and the pressure of the second crystallizer is controlled at 0.05 MPaG, to obtain oxidation slurry IIIf.

[0168] The oxidation slurry IIIf is passed into the oxidation pressure filter 104 for filtration and washing. The filtration area is one partition, and the washing is divided into three partitions. The purified methanol washing liquid containing 1.5% water enters from the last washing area, and is finally discharged from the first washing area after three-stage washing. The filtered mother liquor is returned to the oxidation reaction system. After the washing liquid is separated by the distillation tower, the methanol is recycled, and the acetic acid is returned to the oxidation reaction system for recycling. The oxidation filter cake g is directly fed into the esterification slurry preparation device 105.

[0169] In the esterification slurry preparation device 105, the esterification circulating solvent o used is a methanol solution containing 1.5% water, and the mass ratio of the solvent to naphthalene dicarboxylic acid is 10:1. The esterification slurry Ih is heated to 180°C by the esterification slurry heating device 106 and then enters the first esterification reactor 107 for esterification to obtain an esterification product Ij. Among them, the catalyst is a mixture of tetrabutyl titanate and trimethyl phosphate, with a mass ratio of 9:1, a content of 5% of the mass of 2,6-NDA, and a residence time of 2 hours.

[0170] The esterification product Ij is introduced into the second esterification reactor 108 to continue the esterification reaction. The second esterification reaction temperature is 200°C and the residence time is 2 hours to obtain the esterification product IIk.

[0171] The esterification product IIk is introduced into the first esterification distillation device 110 to remove light components, and the operating temperature of the tower bottom is 210°C; the tower bottom liquid is sent to the second esterification distillation device 110 to remove heavy components, and the tower bottom operating temperature is 270°C and the operating pressure is -0.09MPaG. The crude dimethyl naphthalene dicarboxylate obtained by the top distillation is sent to the recrystallization device 111;

[0172] The recrystallization solvent is recycled methanol containing 2.8% water, the solvent ratio is 7:1, the dissolution temperature is 175°C, the residence time is 60 minutes, and after dissolution, it is crystallized in a two-stage crystallizer with an operating pressure distribution of 1 MPaG and 0.06 MPaG. After recrystallization, the esterification product slurry l is obtained.

[0173] The esterification product slurry l is passed through the esterification rotary pressure filter for treatment, and the flash steam is distilled and the methanol is recycled.

[0174] The esterification product slurry l is sent to the rotary pressure filter for filtration, washing and dehumidification. The filtration area is one partition, the washing area is divided into three partitions, and the dehumidification area is one partition. The purified methanol washing liquid with a water content of 2.8% enters from the last washing area, and is finally discharged from the first washing area after three-stage washing. After the mother liquor and washing liquid are separated in the distillation tower, the methanol is recycled.

[0175] The esterification filter cake m passes through the dehumidification zone to reduce the moisture content to 8%, and is fed to the drying device 113 for drying to obtain a high-purity 2,6-NDC product with a purity of 99.7%.

[0176] The oxidized tail gas is sent to the serially connected steam generator 116 to recover energy by-product steam, and 0.35MPaG, 0.18MPaG, and 0.05MPaG steam are produced respectively. After gas-liquid separation, the gas phase is cooled to 40°C by a circulating water cooler 118, and the tail gas is then sprayed with flushing acid and deionized water and then subjected to catalytic oxidation (CATOX) treatment before being discharged in compliance with the standards. The oxidizing solvent in the oxidation device is dehydrated in a dehydration tower 120, and the concentrated acid obtained is returned to the oxidation system for recycling, and the wastewater containing trace amounts of acid is discharged for sewage treatment.

[0177] In the process of producing 2,6-NDA by oxidation + two-stage deep oxidation in this embodiment, the impurity content is low and the consumption of raw and auxiliary materials is low; the oxidation slurry adopts a one-step rotary pressure filtration process with a short process flow, low energy consumption, small footprint and low investment; the two-step esterification method has a high esterification rate and few product impurities; distillation + recrystallization + rotary pressure filtration is used for purification, and the product has high purity and good hue.

[0178] In summary, the present invention is suitable for industrial production of high-purity dimethyl naphthalate using dialkylnaphthalene as raw material and adopting deep oxidation and cascade esterification combined technology.

[0179] Although the description of the present invention has been quite detailed and has been described in particular with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, so as to effectively cover the intended scope of the present invention. In addition, the present invention is described above with the embodiments foreseeable by the inventors, and its purpose is to provide a useful description, and those non-substantial changes to the present invention that are not currently foreseen may still represent equivalent changes of the present invention.

[0180] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0181] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for producing dimethyl naphthalate, characterized in that: The method comprises: In an oxidation reactor, dialkylnaphthalene, catalyst I and solvent are oxidized with oxygen-containing gas under a first oxidation condition to obtain oxidation slurry I; In a deep oxidation reactor, the oxidized slurry I is deeply oxidized under a second oxidation condition to obtain an oxidized slurry II; In an oxidation crystallization device, the oxidation slurry II is crystallized under a first crystallization condition to obtain oxidation slurry III; In an oxidation pressure filter, filtering and washing the oxidation slurry III to obtain an oxidation filter cake; In the esterification slurry preparation device, the oxidation filter cake and the esterification circulating solvent are prepared into esterification slurry I according to the mass ratio of the naphthalene dicarboxylic acid and the methanol; In an esterification slurry heating device, the esterification slurry I is heated to obtain esterification slurry II; In a first esterification reactor, the esterification slurry II, methanol and catalyst II are esterified under the first esterification conditions to obtain an esterification product I; In a second esterification reactor, the esterification product I is re-esterified under a second esterification condition to obtain an esterification product II; In the esterification purification device, the esterification product II is purified to obtain an esterification product slurry; In an esterification filtration device, the esterification product slurry is filtered, washed and dehumidified to obtain an esterification filter cake; In a drying device, the esterification filter cake is dried to obtain dimethyl naphthalate product.

2. The method according to claim 1, characterized in that The oxidation slurry III is filtered and washed in the oxidation pressure filter to obtain an oxidation filter cake, comprising: In the oxidation pressure filter, the oxidation slurry III passes through the filtration zone and multi-stage washing zone of the oxidation pressure filter in sequence to obtain an oxidation filter cake and a filtrate; The filtrate is treated by the oxidation solvent separation unit to obtain a mother liquor, a washing liquid and a waste liquor; the mother liquor and the washing liquid are circulated to the oxidation reactor for repeated utilization, and the waste liquor is discharged for sewage treatment.

3. The method according to claim 1, characterized in that In the esterification purification device, the esterification product II is purified to obtain an esterification product slurry, comprising: In the esterification distillation device, the esterification product II is separated into light and heavy components to obtain light components, products, and heavy components; the light components and products are then recrystallized in a recrystallization device to obtain an esterification product slurry; Alternatively, the esterification product II is recrystallized in a recrystallization device to obtain a recrystallized esterification product II; the recrystallized esterification product II is then distilled in an esterification distillation device to remove light and heavy components to obtain an esterification product slurry.

4. The method according to claim 3, characterized in that In the recrystallization device, the recrystallization solvent is methanol; the mass ratio of the methanol to the esterification product II is 3:1 to 20:

1.

5. The method according to claim 1, characterized in that In the oxidation reactor, dialkylnaphthalene, catalyst I and solvent are oxidized with oxygen-containing gas under first oxidation conditions to obtain oxidation slurry I, comprising: The catalyst I is selected from a catalyst system containing cobalt, manganese, and bromine or a ligand structure catalyst system formed by cobalt and one or more metals selected from vanadium, molybdenum, nickel, and tungsten, and the cobalt ion concentration is 300ppm to 1500ppm; The mass ratio of the solvent to the dialkylnaphthalene is 3:1 to 20:1; The solvent is selected from a mixture of C2-C6 monocarboxylic acid and water, wherein the water content is 5-20 wt%; The first oxidation conditions are: oxidation temperature of 160-205°C, pressure of 0.7-3MPaG, and residence time of 30-90min; The oxygen-containing gas is selected from one of air, oxygen, oxygen-deficient gas or oxygen-enriched gas.

6. The method according to claim 1, characterized in that The second oxidation conditions are: oxidation temperature of 190-250° C., pressure of 1.0-4.0 MPaG, and residence time of 30-150 min.

7. The method according to claim 1, characterized in that The first crystallization condition is: crystallization pressure -0.05 to 0.1 MPaG.

8. The method according to claim 1, characterized in that The mass ratio of the naphthalene dicarboxylic acid to the methanol is 3:1 to 20:

1.

9. The method according to claim 1, characterized in that: In the first esterification reactor, the esterification slurry II, methanol and catalyst II are esterified under the first esterification conditions to obtain an esterification product I, including: The catalyst II is selected from one or more of benzenesulfonic acid, tetrabutyl titanate, tributyl phosphate, imidazole or pyridine acidic ionic liquids; The first esterification conditions are: esterification temperature 170-280° C., time 1-4 h.

10. The method according to claim 1, characterized in that The second esterification conditions are: esterification temperature 150-210° C., time 1-4 h.

11. The method according to claim 1, characterized in that: The moisture content of the esterification filter cake is 5-15%.

12. A system for producing dimethyl naphthalate, characterized in that: The system is used to implement the method described in any one of claims 1 to 11, comprising: an oxidation reactor, a deep oxidation reactor, an oxidation crystallization device, an oxidation pressure filter, an esterification slurry preparation device, an esterification slurry heating device, a first esterification reactor, a second esterification reactor, an esterification purification device, an esterification filtering device and a drying device; The oxidation reactor is connected to the deep oxidation reactor and is used to deeply oxidize the incompletely oxidized dialkylnaphthalene and the intermediate products in the oxidation slurry I to obtain the oxidation slurry II; The deep oxidation reactor is connected to the oxidation crystallization device, and the oxidation crystallization device is connected to the oxidation pressure filter, which is used to filter and wash the oxidation slurry III to obtain the oxidation filter cake; The oxidation pressure filter is connected to the esterification slurry preparation device, and is used to prepare the oxidation filter cake into the esterification slurry I according to a set mass ratio; The esterification slurry preparation device is connected to the esterification slurry heating device and is used to preheat the esterification slurry I; The esterification slurry heating device is connected to the first esterification reactor, and the first esterification reactor is connected to the second esterification reactor, and is used for secondary esterification of the monoester by-product contained in the esterification product I to generate the esterification product II; The second esterification reactor is connected to the esterification purification device to purify the esterification product II to obtain the esterification product slurry; The esterification purification device is connected to the esterification filtration device and is used for filtering, washing and dehumidifying to obtain an esterification filter cake; The esterification filtering device is connected to the drying device and is used to dry the esterification filter cake to obtain a dimethyl naphthalate product.

13. The system for producing dimethyl naphthalate according to claim 12, characterized in that: The esterification purification device includes an esterification rectification device and a recrystallization device; The esterification distillation device is used to separate the light and heavy components in the esterification product II; The recrystallization device is used to remove light components and some impurities contained in the esterification product II.

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