Preparation process of high-purity methylal
By generating crude formaldehyde products in the atmospheric catalytic distillation tower, and performing multi-stage distillation in the primary and secondary pressurized distillation towers, high-purity formaldehyde is finally produced by dehydration treatment. The problem of low purity of formaltal in the prior art was solved, and high purity preparation of formaltal is achieved.
Patent Information
- Application Number
- CN202411735699.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-02-14
AI Technical Summary
In the prior art, the purity of acetal is low, resulting in limited application in many industries.
A high-purity formaldehyde preparation process is adopted, which includes the generation of crude formaldehyde in an atmospheric catalytic distillation tower, and multi-stage distillation through a primary pressurized distillation tower and a secondary pressurized distillation tower, and finally through Dehydration treatment to produce high-purity formaldehyde.
The purity of methylacetal has been achieved to reach more than 99.999%, meeting the high purity needs such as electronic grade and chromatographic grade.
Smart Images
Figure CN119425530A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of chemical production, and in particular to a process for preparing high-purity methylal. Background Art
[0002] Methylal, also known as dimethoxymethane, has the molecular formula CH3OCH2OCH3. It is a colorless, non-toxic, environmentally friendly chemical product that can be used as an organic synthesis intermediate, solvent and diesel additive. It is an environmentally friendly product that can replace toxic and harmful solvents and reduce air pollution.
[0003] In industry, methylal is usually obtained by reacting methanol and formaldehyde aqueous solution catalyzed by an acidic catalyst. Since methylal and methanol can form an azeotrope, theoretically, conventional distillation separation under normal pressure can only obtain a product with a methylal mass fraction of about 92-93%. Methanol, as an impurity, has a high content and relatively high toxicity, which limits the application of methylal in many industries. Summary of the invention
[0004] The main purpose of the invention is to provide a high-purity methylal preparation process, aiming to solve the problem of low purity of the methylal product obtained by the existing preparation process.
[0005] To achieve the above object, a high-purity methylal preparation process proposed by the present invention comprises the following steps:
[0006] S10, methanol and formaldehyde aqueous solution are transported to a normal pressure catalytic distillation tower and react to generate methylal, a normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure catalytic distillation tower, and waste water is produced from the bottom of the tower, the normal pressure methylal-methanol azeotrope is condensed to form a normal pressure methylal-methanol blend, part of which is refluxed to the normal pressure catalytic distillation tower, and the rest is transported to a primary pressure distillation tower;
[0007] S20, the methylal-methanol blend transported to the first-stage pressure distillation tower is operated under pressure, the pressurized methylal-methanol azeotrope is extracted from the top of the first-stage pressure distillation tower, and the methylal solution is extracted from the bottom of the tower, and the methylal solution is transported to the second-stage pressure distillation tower, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of it is refluxed to the first-stage pressure distillation tower;
[0008] S30, the methylal solution transported to the secondary pressure distillation tower is under pressure operation, the pressurized methylal-methanol azeotrope is produced from the top of the secondary pressure distillation tower, and the methylal solution is produced from the bottom of the tower, the methylal solution is dehydrated to obtain high-purity methylal, the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of it is refluxed to the secondary pressure distillation tower.
[0009] Optionally, in step S10, the methanol and formaldehyde aqueous solution in the atmospheric pressure catalytic distillation tower react to generate methylal under the action of a solid acid catalyst, and the solid acid catalyst is selected from one of Amberstly-70 sulfonic acid resin solid acid catalyst, HZSM-5 molecular sieve, HBeta zeolite molecular sieve and HMCM-22 zeolite molecular sieve.
[0010] Optionally, in step S10, the atmospheric pressure catalytic distillation tower is a plate tower, and the number of effective plates of the atmospheric pressure catalytic distillation tower is 60 to 100.
[0011] Preferably, in step S10, the number of effective plates of the atmospheric pressure catalytic distillation tower is 65 to 80.
[0012] Further preferably, in step S10, the number of effective plates of the atmospheric pressure catalytic distillation tower is 70.
[0013] Optionally, in step S10, the top temperature of the atmospheric pressure catalytic distillation tower is 40-50° C., and the bottom temperature of the tower is 100-110° C.;
[0014] In the step S20, the operating pressure of the first-stage pressurized distillation tower is 0.7-1.5 MPa, the tower top temperature is 110-120° C., and the tower bottom temperature is 120-130° C.;
[0015] In the step S30, the operating pressure of the two-stage pressure distillation tower is 1.0-2.0 MPa, the tower top temperature is 125-150°C, and the tower bottom temperature is 135-160°C.
[0016] Optionally, the step S30 further includes the following steps:
[0017] S40, the remaining part of the methylal-methanol blend in step S20 and step S30 is transported to a normal pressure recovery distillation tower, the normal pressure recovery distillation tower is subjected to normal pressure distillation operation, and the normal pressure methylal-methanol azeotrope is produced from the top of the tower, and the methanol solution is produced from the bottom of the tower. The normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure recovery distillation tower, and is condensed to form a normal pressure methylal-methanol blend, part of which is refluxed to the normal pressure recovery distillation tower, and the rest is transported to the first-level pressurized distillation tower.
[0018] Optionally, in the step S20, the purity of methylal in the formed methylal-methanol blend is 80-85%;
[0019] In the step S30, the purity of methylal in the formed methylal-methanol blend is 75-80%.
[0020] Optionally, in step S40, the top temperature of the atmospheric pressure recovery distillation tower is 40-45°C, and the bottom temperature is 60-65°C.
[0021] Optionally, in the step S10 and the step S40, the purity of methylal in the atmospheric pressure methylal-methanol blend formed is 90-93%.
[0022] Optionally, in the step S20, the purity of methylal in the methylal solution extracted from the bottom of the first-stage pressurized distillation tower is ≥99.5%;
[0023] In the step S30, the purity of methylal in the methylal solution extracted from the bottom of the secondary pressure distillation tower is ≥99.95%, and the purity of methylal in the obtained high-purity methylal is ≥99.999%.
[0024] Optionally, the reflux ratio of the atmospheric pressure catalytic distillation tower, the first-stage pressurized distillation tower, and the second-stage pressurized distillation tower is 1-5.
[0025] In the technical scheme of the present invention, in step S10, in a normal pressure catalytic distillation tower, methanol and formaldehyde aqueous solution are subjected to an aldol condensation reaction under the catalytic action of an acidic catalyst to generate methylal, and after distillation treatment, a normal pressure methylal-methanol azeotrope is extracted from the top of the normal pressure catalytic distillation tower, and the methylal-methanol azeotrope is condensed to form a normal pressure methylal-methanol blend, and part of the methylal-methanol blend is refluxed to the top of the normal pressure catalytic distillation tower, and the remaining part of the methylal-methanol blend is transported to a primary pressurized distillation tower. The water generated by the reaction and the water brought in by the formaldehyde aqueous solution are gathered at the bottom of the tower, extracted from the bottom of the normal pressure catalytic distillation tower, and discharged as process wastewater.
[0026] In step S20, the methylal-methanol blend transported to the first-stage pressure distillation tower is subjected to pressure distillation under pressure operation, and the pressurized methylal-methanol azeotrope is extracted from the top of the first-stage pressure distillation tower, and the methylal solution is extracted from the bottom of the first-stage pressure distillation tower. The methylal solution is transported to the second-stage pressure distillation tower, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend. Part of the methylal-methanol blend is refluxed to the first-stage pressure distillation tower, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower.
[0027] In step S30, the methylal solution transported to the secondary pressure distillation tower is further subjected to pressure distillation under pressure operation, and the pressurized methylal-methanol azeotrope is extracted from the top of the secondary pressure distillation tower, and the methylal solution with higher purity is extracted from the bottom of the secondary pressure distillation tower. The high-purity methylal solution is dehydrated to obtain high-purity methylal, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend. Part of the methylal-methanol blend is refluxed into the secondary pressure distillation tower, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower.
[0028] The technical solution of the present invention uses methanol and formaldehyde aqueous solution as raw materials, reacts in a normal pressure catalytic distillation tower to generate a crude methylal product, and adopts a first-level pressurized distillation tower and a second-level pressurized distillation tower to distill the crude methylal product. No extractant needs to be added during the preparation process, and a methylal product with a purity of more than 99.95% can be prepared. After dehydration, a methylal product with a purity of more than 99.999% can be prepared, so as to better meet the use requirements of electronic grade and chromatographic grade products. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.
[0030] Figure 1 The present invention provides a schematic structural diagram of a methylal preparation device according to an embodiment of the present invention.
[0031] Description of Figure Numbers:
[0032] 1. Atmospheric pressure catalytic distillation tower; 11. First condenser; 12. First reflux tank; 13. First reflux pump; 14. First reflux pipe; 15. First discharge pipe; 16. First distillation section; 17. First reaction section; 18. First stripping section; 19. First reboiler; 110. Wastewater extraction pipe; 111. First feed inlet; 2. One-stage pressurized distillation tower; 21. Second gas outlet pipe; 22. Second liquid inlet pipe; 23. Second reflux tank; 24. Second reflux pump; 25. Second reflux pipe; 26. Second discharge pipe; 27. Second distillation section; 28. Second separation section; 29. Second stripping section; 210. Second feed inlet; 211. Second reboiler; 212. Second methylal solution extraction pipe; 3. Second stage pressurized distillation tower; 31, third gas outlet pipe; 32, third liquid inlet pipe; 33, third reflux tank; 34, third reflux pump; 35, third reflux pipe; 36, third discharge pipe; 37, third distillation section; 38, third separation section; 39, third feed inlet; 310, third stripping section; 311, third reboiler; 312, third methylal solution extraction pipe; 313, dehydrator; 4, atmospheric pressure recovery distillation tower; 41, fourth condenser; 42, fourth reflux tank; 43, fourth reflux pump; 44, fourth reflux pipe; 45, fourth discharge pipe; 46, fourth distillation section; 47, fourth separation section; 48, fourth stripping section; 49, fourth reboiler; 410, methanol extraction pipe; 411, fourth feed inlet.
[0033] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0035] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.
[0036] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.
[0037] Industrially, methylal is usually obtained by reacting methanol and formaldehyde aqueous solution with an acidic catalyst. Since methylal and methanol can form an azeotrope, theoretically, conventional distillation separation under normal pressure can only obtain a product with a methylal mass fraction of about 92-93%. Methanol, as an impurity, has a high content and relatively high toxicity, which limits the application of methylal in many industries. In view of this, the present invention proposes a high-purity methylal preparation process to solve the problem of low purity of the methylal product obtained by the existing preparation process.
[0038] See also Figure 1 In one embodiment of the present invention, the process for preparing high-purity methylal comprises the following steps:
[0039] S10, methanol and formaldehyde aqueous solution are transported to a normal pressure catalytic distillation tower 1 and react to generate methylal, a normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure catalytic distillation tower 1, and waste water is produced from the bottom of the tower, the normal pressure methylal-methanol azeotrope is condensed to form a normal pressure methylal-methanol blend, part of which is refluxed to the normal pressure catalytic distillation tower 1, and the rest is transported to a primary pressure distillation tower 2;
[0040] S20, the methylal-methanol blend transported to the first-stage pressure distillation tower 2 is operated under pressure, the pressurized methylal-methanol azeotrope is extracted from the top of the first-stage pressure distillation tower 2, and the methylal solution is extracted from the bottom of the tower, and the methylal solution is transported to the second-stage pressure distillation tower 3, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, which is partially refluxed to the first-stage pressure distillation tower 2;
[0041] S30, the methylal solution transported to the secondary pressure distillation tower 3 is under pressure operation, the pressurized methylal-methanol azeotrope is extracted from the top of the secondary pressure distillation tower 3, and the methylal solution is extracted from the bottom of the tower, the methylal solution is dehydrated to obtain high-purity methylal, the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of it is refluxed to the secondary pressure distillation tower 3.
[0042] By adopting the above technical scheme, in step S10, in the atmospheric pressure catalytic distillation tower 1, methanol and formaldehyde aqueous solution undergo an aldol condensation reaction under the action of an acidic catalyst to generate methylal, and after distillation treatment, the atmospheric pressure methylal-methanol azeotrope is extracted from the top of the atmospheric pressure catalytic distillation tower 1, and the methylal-methanol azeotrope is condensed to form an atmospheric pressure methylal-methanol blend, part of the methylal-methanol blend is refluxed to the top of the atmospheric pressure catalytic distillation tower 1, and the rest of the methylal-methanol blend is transported to the primary pressurized distillation tower 2. The water generated by the reaction and the water brought in by the formaldehyde aqueous solution are collected at the bottom of the tower, extracted from the bottom of the atmospheric pressure catalytic distillation tower 1, and discharged as process wastewater.
[0043] In step S20, the methylal-methanol blend transported to the first-level pressurized distillation tower 2 is subjected to pressurized distillation under pressure operation, and the pressurized methylal-methanol azeotrope is extracted from the top of the first-level pressurized distillation tower 2, and the methylal solution is extracted from the bottom of the first-level pressurized distillation tower 2. The methylal solution is transported to the second-level pressurized distillation tower 3, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend. Part of the methylal-methanol blend is refluxed to the first-level pressurized distillation tower 2, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower 4.
[0044] In step S30, the methylal solution transported to the secondary pressure distillation tower 3 is further subjected to pressure distillation under pressure operation, and the pressurized methylal-methanol azeotrope is extracted from the top of the secondary pressure distillation tower 3, and the methylal solution with higher purity is extracted from the bottom of the secondary pressure distillation tower 3. The high-purity methylal solution is dehydrated to obtain high-purity methylal, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend. Part of the methylal-methanol blend is refluxed into the secondary pressure distillation tower 3, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower 4.
[0045] In the technical scheme of the present invention, methanol and formaldehyde aqueous solution are used as raw materials, and a crude methylal product is generated by reaction in a normal pressure catalytic distillation tower 1. The crude methylal product is purified by a first-stage pressurized distillation tower 2 and a second-stage pressurized distillation tower 3, so that a methylal product with a purity of more than 99.95% can be obtained. After dehydration, a methylal product with a purity of more than 99.999% can be obtained, so as to better meet the use requirements of electronic grade and chromatographic grade products.
[0046] Furthermore, the step S30 further includes the following steps: S40, the remaining part of the methylal-methanol blend in the step S20 and the step S30 is transported to a normal pressure recovery distillation tower 4, the normal pressure recovery distillation tower 4 is subjected to normal pressure distillation operation, and the normal pressure methylal-methanol azeotrope is produced from the top of the tower, and the methanol solution is produced from the bottom of the tower, the normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure recovery distillation tower 4, and the normal pressure methylal-methanol blend is formed after condensation, part of which is refluxed to the normal pressure recovery distillation tower 4, and the rest is transported to the first-stage pressurized distillation tower 2.
[0047] By adopting the above technical scheme, the remaining part of the methylal-methanol blend in step S20 and step S30 is transported to the atmospheric pressure recovery distillation tower 4, the atmospheric pressure recovery distillation tower 4 is subjected to atmospheric distillation operation, the atmospheric pressure recovery distillation tower 4 extracts the atmospheric pressure methylal-methanol azeotrope, the atmospheric pressure recovery distillation tower 4 extracts the methanol solution at the bottom, the atmospheric pressure methylal-methanol azeotrope is condensed to form the methylal-methanol blend, part of the methylal-methanol blend is refluxed to the atmospheric pressure recovery distillation tower 4, and the remaining part of the methylal-methanol blend is transported to the primary pressure distillation tower 2 for further distillation. The methanol solution extracted at the bottom of the tower can be transported to the atmospheric pressure catalytic distillation tower 1 as a source of methanol.
[0048] It should be noted that the atmospheric catalytic distillation tower 1 is a plate tower with an effective number of plates of 60 to 100. From top to bottom, the atmospheric catalytic distillation tower 1 includes a first top condensation section, a first distillation section 16, a first reaction section 17, a first stripping section 18, and a first reboiler 19. The first top condensation section includes a first condenser 11, a first reflux tank 12, a first reflux pump 13 and a first reflux pipe 14 connected in sequence. The first condenser 11 is connected to the steam outlet at the top of the atmospheric catalytic distillation tower 1 through a pipeline, and the liquid outlet end of the first reflux pipe 14 is connected to the liquid return port at the top of the atmospheric catalytic distillation tower 1. The feed port of the first reboiler 19 is connected to the discharge port at the bottom of the atmospheric catalytic distillation tower 1 through a pipeline, and the discharge port of the first reboiler 19 is connected to the return port at the bottom of the atmospheric catalytic distillation tower 1 through a pipeline. The first feed port 111 is located in the middle between the first distillation section 16 and the first reaction section 17. Methanol and formaldehyde aqueous solution enter the atmospheric catalytic distillation tower 1 through the first feed port 111. The molar ratio of methanol to formaldehyde in the fresh formaldehyde aqueous solution and fresh methanol fed into the first feed port 111 is (2-2.5):1, and the mass fraction of formaldehyde in the fresh formaldehyde aqueous solution fed is 20-50% (purity is 20-50%), and the purity of the fresh methanol fed is 99.9%. The first reaction section 17 is provided with a solid acid catalyst. A wastewater extraction pipe 110 is also provided at the bottom of the atmospheric catalytic distillation tower 1. The wastewater extraction pipe 110 is provided with a first water pump, and the wastewater at the bottom of the atmospheric catalytic distillation tower 1 is extracted through the wastewater extraction pipe 110.
[0049] It is understood that the methylal-methanol azeotrope at atmospheric pressure is extracted from the top of the atmospheric catalytic distillation tower 1, and after condensation in the first top condensation section, a methylal-methanol blend is formed. The solid acid catalyst is selected from at least one of Amberstly-70 sulfonic acid resin solid acid catalyst, HZSM-5 molecular sieve, HBeta zeolite molecular sieve and HMCM-22 zeolite molecular sieve.
[0050] Further, the first-stage pressurized distillation tower 2 is a plate tower, and the number of effective plates is 30 to 50. The first-stage pressurized distillation tower 2 includes a second top condensation section, a second distillation section 27, a second separation section 28, a second stripping section 29, and a second reboiler 211 arranged in sequence. The second top condensation section includes a second gas outlet pipe 21, a second liquid inlet pipe 22, a second reflux tank 23, a second reflux pump 24, and a second reflux pipe 25 connected in sequence, one end of the second gas outlet pipe 21 is connected to the steam outlet at the top of the first-stage pressurized distillation tower 2, the other end of the second gas outlet pipe 21 is connected to the heat exchange medium inlet of the first reboiler 19, one end of the second liquid inlet pipe 22 is connected to the heat exchange medium outlet of the first reboiler 19, the other end of the second liquid inlet pipe 22 is connected to the second reflux tank 23, and the liquid outlet end of the second reflux pipe 25 is connected to the liquid return port at the top of the first-stage pressurized distillation tower 2. The feed port of the second reboiler 211 is connected to the discharge port at the bottom of the first-stage pressurized distillation tower 2 through a pipeline, and the discharge port of the second reboiler 211 is connected to the return port at the bottom of the first-stage pressurized distillation tower 2 through a pipeline; the second reboiler 211 is also provided with a heat exchange medium inlet and a heat exchange medium outlet, and the heating steam enters the second reboiler 211 through the heat exchange medium inlet to exchange heat with the material in the second reboiler 211, and then flows out through the heat exchange medium outlet. The second feed port 210 is located in the middle between the second distillation section 27 and the second separation section 28, and the second feed port 210 is connected to the first discharge pipe 15. The second reflux pipe 25 is branched with a second discharge pipe 26, and the second discharge pipe 26 is connected to the fourth feed port 411 on the atmospheric recovery distillation tower 4. A second methylal solution extraction pipe 212 is also provided at the bottom of the first-stage pressurized distillation tower 2 . A second water pump is provided on the second methylal solution extraction pipe 212 . The second methylal solution extraction pipe 212 is connected to the third feed port 39 on the second-stage pressurized distillation tower 3 .
[0051] It can be understood that the methylal-methanol azeotrope extracted from the top of the first-stage pressurized distillation tower 2 is transported to the heat exchange medium inlet of the first reboiler 19 through the second outlet pipe 21, and then enters the first reboiler 19 to provide a heat source for the first reboiler 19. The methylal-methanol azeotrope is condensed after heat exchange to form a methylal-methanol blend. The methylal-methanol blend flows out from the heat exchange medium outlet of the first reboiler 19, flows through the second reflux tank 23, and then part of the methylal-methanol blend is refluxed to the top of the first-stage pressurized distillation tower 2 through the second reflux pipe 25, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower 4 through the second discharge pipe 26.
[0052] The methylal solution deposited at the bottom of the first-stage pressure distillation tower 2 is taken out through the second methylal solution extraction pipe 212 and transported to the second-stage pressure distillation tower 3 for further pressure distillation to obtain a high-purity methylal product.
[0053] Further, the secondary pressure distillation tower 3 is a plate tower, and the number of effective plates is 30 to 50. The secondary pressure distillation tower 3 includes a third tower top condensation section, a third distillation section 37, a third separation section 38, a third stripping section 310, and a third reboiler 311 arranged in sequence. The third tower top condensation section includes a third gas outlet pipe 31, a third liquid inlet pipe 32, a third reflux tank 33, a third reflux pump 34 and a third reflux pipe 35 connected in sequence, one end of the third gas outlet pipe 31 is connected to the steam outlet at the top of the secondary pressure distillation tower 3, the other end of the third gas outlet pipe 31 is connected to the heat exchange medium inlet of the fourth reboiler 49 at the bottom of the atmospheric recovery distillation tower 4, one end of the third liquid inlet pipe 32 is connected to the heat exchange medium outlet of the fourth reboiler 49, the other end of the third liquid inlet pipe 32 is connected to the third reflux tank 33, and the liquid outlet end of the third reflux pipe 35 is connected to the liquid return port at the top of the secondary pressure distillation tower 3. The feed port of the third reboiler 311 is connected to the discharge port at the bottom of the secondary pressurized distillation tower 3 through a pipeline, and the discharge port of the third reboiler 311 is connected to the return port at the bottom of the secondary pressurized distillation tower 3 through a pipeline; the third reboiler 311 is also provided with a heat exchange medium inlet and a heat exchange medium outlet, and the heating steam enters the third reboiler 311 through the heat exchange medium inlet to exchange heat with the material in the third reboiler 311, and then flows out through the heat exchange medium outlet. The third feed port 39 is located in the middle position between the third stripping section 310 and the third separation section 38, and the third feed port 39 is connected to the second methylal solution extraction pipe 212. The third reflux pipe 35 is branched with a third discharge pipe 36, and the discharge end of the third discharge pipe 36 is connected to the fourth feed port 411 on the atmospheric recovery distillation tower 4. A third methylal solution extraction pipe 312 is also provided at the bottom of the secondary pressurized distillation tower 3, and a third water pump is provided on the third methylal solution extraction pipe 312. The liquid outlet end of the third methylal solution extraction pipe 312 is connected to a dehydrator 313. The methylal solution extracted from the bottom of the secondary pressurized distillation tower 3 is dehydrated by the dehydrator 313 to obtain a methylal product with a purity of more than 99.999%.
[0054] It can be understood that the pressurized methylal-methanol azeotrope extracted from the top of the secondary pressure distillation tower 3 is transported to the heat exchange medium inlet of the fourth reboiler 49 through the third outlet pipe 31, and then enters the fourth reboiler 49 to provide a heat source for the fourth reboiler 49. The methylal-methanol azeotrope is condensed after heat exchange to form a methylal-methanol blend. The methylal-methanol blend flows out from the heat exchange medium outlet of the fourth reboiler 49, flows through the third reflux tank 33, and part of the methylal-methanol blend is refluxed to the top of the secondary pressure distillation tower 3 through the third reflux pipe 35, and the remaining part of the methylal-methanol blend is transported to the atmospheric pressure recovery distillation tower 4 through the third discharge pipe 36.
[0055] The dehydrator 313 is provided with a molecular sieve inside, and the molecular sieve can absorb the water in the methylal solution to further purify the methylal, so as to obtain a methylal product with a purity of more than 99.999%.
[0056] Furthermore, the atmospheric recovery distillation tower 4 is a plate tower with an effective number of plates of 30 to 50. In the direction from top to bottom, the atmospheric recovery distillation tower 4 includes a fourth top condensation section, a fourth distillation section 46, a fourth separation section 47, a fourth stripping section 48, and a fourth reboiler 49. The fourth top condensation section includes a fourth condenser 41, a fourth reflux tank 42, a fourth reflux pump 43 and a fourth reflux pipe 44 connected in sequence by pipelines, the fourth condenser 41 is connected to the steam outlet at the top of the atmospheric recovery distillation tower 4 through a pipeline, and the liquid outlet end of the fourth reflux pipe 44 is connected to the liquid return port at the top of the atmospheric recovery distillation tower 4. A fourth discharge pipe 45 is provided on the fourth reflux pipe 44, and the fourth discharge pipe 45 is connected to the second feed port 210 on the first-stage pressurized distillation tower 2. The feed port of the fourth reboiler 49 is connected to the discharge port at the bottom of the atmospheric recovery distillation tower 4 through a pipeline, and the discharge port of the fourth reboiler 49 is connected to the return port at the bottom of the atmospheric recovery distillation tower 4 through a pipeline. A fourth feed port 411 is provided on the atmospheric recovery distillation tower 4, and the feed port is located in the middle between the fourth distillation section 46 and the fourth separation section 47, and the discharge end of the second discharge pipe 26 and the discharge end of the third discharge pipe 36 are both connected to the fourth feed port 411. A methanol extraction pipe 410 is also provided at the bottom of the atmospheric recovery distillation tower 4, and a fourth water pump is provided on the methanol extraction pipe 410, and the discharge end of the methanol extraction pipe 410 is connected to the first feed port 111. The operating pressure of the atmospheric recovery distillation tower 4 is atmospheric pressure, the tower top temperature is 40-45°C, and the tower bottom temperature is 60-65°C. The reflux ratio of the atmospheric recovery distillation tower 4 is 1-5.
[0057] It can be understood that the remaining methylal-methanol blend extracted from the primary pressure distillation tower 2 and the secondary pressure distillation tower 3 is transported to the atmospheric pressure recovery distillation tower 4 through the fourth feed port 411, and the atmospheric pressure recovery distillation tower 4 is operated by atmospheric distillation. The top of the atmospheric pressure recovery distillation tower 4 extracts the atmospheric pressure methylal-methanol azeotrope, and the bottom of the atmospheric pressure recovery distillation tower 4 extracts the methanol solution. The atmospheric pressure methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of the methylal-methanol blend is refluxed to the atmospheric pressure recovery distillation tower 4, and the remaining part of the methylal-methanol blend is transported to the primary pressure distillation tower 2 for further separation. The methanol solution extracted from the bottom of the tower is transported to the first feed port 111 as a source of raw materials for the atmospheric pressure catalytic distillation tower 1 to achieve the purpose of material recycling.
[0058] Furthermore, in the step S10, the operating pressure of the atmospheric catalytic distillation tower 1 is atmospheric pressure, the tower top temperature is 40-50°C, and the tower bottom temperature is 100-110°C; in the step S20, the operating pressure of the first-stage pressurized distillation tower 2 is 0.7-1.5MPa, the tower top temperature is 110-120°C, and the tower bottom temperature is 120-130°C; in the step S30, the operating pressure of the second-stage pressurized distillation tower 3 is 1-2MPa, the tower top temperature is 125-150°C, and the tower bottom temperature is 135-160°C.
[0059] By adopting the above technical solution, a high-purity methylal product is obtained by controlling the operating pressure and operating temperature of the atmospheric pressure catalytic distillation tower 1, the first-stage pressurized distillation tower 2, and the second-stage pressurized distillation tower 3.
[0060] Furthermore, in the step S20, the purity of methylal in the methylal-methanol blend is 80-85%; in the step S30, the purity of methylal in the methylal-methanol blend is 75-80%.
[0061] Furthermore, in the step S10 and the step S40, the purity of methylal in the atmospheric pressure methylal-methanol blend formed is 90-93%.
[0062] Furthermore, in the step S20, the purity of methylal in the methylal solution extracted from the bottom of the first-stage pressure distillation tower 2 is ≥99.5%.
[0063] Furthermore, the reflux ratios of the atmospheric pressure catalytic distillation tower 1, the first-stage pressure distillation tower 2, and the second-stage pressure distillation tower 3 are 1 to 5. By controlling the reflux ratios of the distillation towers, the distillation effect of the distillation towers can be better guaranteed.
[0064] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.
[0065] Example 1
[0066] Combination Figure 1 This embodiment provides a process for preparing high-purity methylal, comprising the following steps:
[0067] S10, fresh formaldehyde aqueous solution containing 40% formaldehyde mass fraction (feed 1), fresh methanol with a purity of 99.9% (feed 2), and feed 3 (methanol solution recovered by atmospheric pressure recovery distillation tower 4, see step S40) enter the atmospheric pressure catalytic distillation tower 1 from the first feed port 111, wherein the flow rate of fresh formaldehyde aqueous solution is 1757.812 kg / h, the flow rate of fresh methanol is 1500 kg / h, and the flow rate of feed 3 is 181.422 kg / h. The first reaction section 17 is filled with 2m 3 Amberstly-70 sulfonic acid resin solid acid catalyst. The inner diameter of the atmospheric catalytic distillation tower 1 is 1000 mm, the number of effective plates is 60, the spacing between two adjacent plates is 300 mm, the number of plates in the first distillation section 16 is 16, the number of plates in the first reaction section 17 is 25, and the number of plates in the first stripping section 18 is 19. The operating pressure of the atmospheric catalytic distillation tower 1 is atmospheric pressure, the reflux ratio is 1.8, the tower top temperature is 42°C, and the tower bottom temperature is 100°C. After the catalytic distillation of the atmospheric pressure catalytic distillation tower 1, the generated methylal-methanol azeotrope is extracted from the tower top, and after condensation, a methylal-methanol blend (methylal in the methylal-methanol blend is 90.6wt%) is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is transported to the first-stage pressurized distillation tower 2 through the first discharge pipe 15 for pressurized distillation, wherein the top discharge of the atmospheric pressure catalytic distillation tower 1 (methylal in the top discharge is 90.6wt%) is extracted at a flow rate of 1962.673kg / h, and then pumped to the first-stage pressurized distillation tower 2. The water generated by the reaction and the water brought in by the formaldehyde aqueous solution are collected at the bottom of the tower, and as process wastewater, are extracted and discharged from the bottom of the first catalytic distillation tower at a flow rate of 1476.561kg / h.
[0068] S20, the methylal-methanol blend transported through the first discharge pipe 15, and the methylal-methanol blend transported through the fourth discharge pipe 45, enter the first-stage pressurized distillation tower 2 through the second feed port 210, wherein the flow rate of the methylal-methanol blend transported by the first discharge pipe 15 refers to step S10, and the flow rate of the methylal-methanol blend transported by the fourth discharge pipe 45 refers to step S40. The inner diameter of the first-stage pressurized distillation tower 2 is 800mm, the number of effective plates is 30, the spacing between two adjacent plates is 300mm, the number of plates in the second distillation section 27 is 9, the number of plates in the second separation section 28 is 11, and the number of plates in the second stripping section 29 is 10. The operating pressure of the first-stage pressurized distillation tower 2 is 0.8MPa, the reflux ratio is 2, the top temperature is 110°C, and the bottom temperature is 120°C. After the pressurized distillation action of the first-stage pressurized distillation tower 2, methylal-methanol azeotrope is generated, and the generated methylal-methanol azeotrope is extracted from the top of the tower, and after condensation, a methylal-methanol blend (methylal in the methylal-methanol blend is 81.9wt%) is formed. Part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the atmospheric pressure recovery distillation tower 4 through the second discharge pipe 26 for distillation, wherein the top discharge of the first-stage pressurized distillation tower 2 (methylal in the top discharge is 81.9wt%) is extracted at a flow rate of 1733.505kg / h, and then pumped to the atmospheric pressure recovery distillation tower 4. The methylal solution (methylal solution, 99.9 wt % methylal) generated after the pressure distillation is collected at the bottom of the tower. The methylal solution at the bottom of the tower is extracted through the second methylal solution extraction pipe 212 at a flow rate of 1788.831 kg / h, and then transported to the secondary pressure distillation tower 3.
[0069] S30, the methylal-methanol blend transported through the second methylal solution extraction pipe 212 enters the secondary pressure distillation tower 3 through the third feed port 39, wherein the flow rate of the methylal-methanol blend transported by the second methylal solution extraction pipe 212 is referred to step S20. The inner diameter of the secondary pressure distillation tower 3 is 800mm, the number of effective plates is 35, the spacing between two adjacent plates is 500mm, the number of plates in the third distillation section 37 is 10, the number of plates in the third separation section 38 is 13, and the number of plates in the third stripping section 310 is 12. The operating pressure of the secondary pressure distillation tower 33 is 1.5MPa, the reflux ratio is 2.6, the top temperature is 130°C, and the bottom temperature is 140°C. After the pressurized distillation action of the secondary pressure distillation tower 3, the generated methylal-methanol azeotrope is extracted from the top of the tower, and after condensation, a methylal-methanol blend (methylal in the methylal-methanol blend is 76.4wt%) is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the atmospheric pressure recovery distillation tower 4 through the third discharge pipe 36 for distillation, wherein the top discharge of the secondary pressure distillation tower 3 (methylal in the top discharge is 76.4wt%) is extracted at a flow rate of 7.58kg / h, and then transported to the atmospheric pressure recovery distillation tower 4. The methylal solution (methylal solution, 99.99wt%) generated after pressure distillation is collected at the bottom of the tower. The methylal solution at the bottom of the tower is extracted through the third methylal solution extraction pipe 312 at a flow rate of 1781.251kg / h, and then transported to the dehydrator 313 equipped with molecular sieves. The molecular sieves can absorb water to obtain high-purity methylal products.
[0070] S40, the methylal-methanol blend transported through the second discharge pipe 26, and the methylal-methanol blend transported through the third discharge pipe 36, enter the atmospheric pressure recovery distillation tower 4 through the fourth feed port 411, wherein the flow rate of the methylal-methanol blend transported by the second discharge pipe 26 refers to step S20, and the flow rate of the methylal-methanol blend transported by the third discharge pipe 36 refers to step S30. The inner diameter of the atmospheric pressure recovery distillation tower 4 is 800mm, the number of effective plates is 30, the spacing between two adjacent plates is 350mm, the number of plates in the fourth distillation section 46 is 9, the number of plates in the fourth separation section 47 is 12, and the number of plates in the fourth stripping section 48 is 9. The operating pressure of the atmospheric pressure recovery distillation tower 4 is atmospheric pressure, the reflux ratio is 1.8, the tower top temperature is 43°C, and the tower bottom temperature is 62°C. The distillation of the atmospheric pressure recovery distillation tower 4 generates methylal-methanol azeotrope, which is extracted from the top of the tower and condensed to form a methylal-methanol blend (methylal 91.4wt% in the methylal-methanol blend), part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the first-stage pressurized distillation tower 2 through the fourth discharge pipe 45 for distillation, wherein the top discharge of the atmospheric pressure recovery distillation tower 4 (methylal 91.4wt% in the top discharge) is extracted at a flow rate of 1559.663kg / h and then transported to the first-stage pressurized distillation tower 2. The methanol solution generated after distillation is collected at the bottom of the tower, and the methanol solution at the bottom of the tower is extracted at a flow rate of 181.422kg / h through the methanol extraction pipe 410 and then transported to the first feed port 111.
[0071] It is measured that in the high-purity methylal product prepared in step S30, the mass fraction of methylal is 99.9991%, and the mass percentages of water and methanol are both less than 10 ppm.
[0072] Example 2
[0073] A process for preparing high-purity methylal comprises the following steps:
[0074] S10, fresh formaldehyde aqueous solution containing 40% formaldehyde mass fraction (feed 1), fresh methanol with a purity of 99.9% (feed 2), and feed 3 (methanol solution recovered by atmospheric pressure recovery distillation tower 4, see step S40) enter the atmospheric pressure catalytic distillation tower 1 from the first feed port 111, wherein the flow rate of fresh formaldehyde aqueous solution is 1757.812 kg / h, the flow rate of fresh methanol is 1500 kg / h, and the flow rate of feed 3 is 181.422 kg / h. The first reaction section 17 is filled with 2m 3Amberstly-70 sulfonic acid resin solid acid catalyst. The inner diameter of the atmospheric catalytic distillation tower 1 is 1000mm, the number of effective plates is 65, the spacing between two adjacent plates is 300mm, the number of plates in the first distillation section 16 is 16, the number of plates in the first reaction section 17 is 30, and the number of plates in the first stripping section 18 is 19. The operating pressure of the atmospheric catalytic distillation tower 1 is atmospheric pressure, the reflux ratio is 1.8, the tower top temperature is 42°C, and the tower bottom temperature is 100°C. After the catalytic distillation of the atmospheric pressure catalytic distillation tower 1, the generated methylal-methanol azeotrope is extracted from the top of the tower, and after condensation, a methylal-methanol blend is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is transported to the first-stage pressurized distillation tower 2 through the first discharge pipe 15 for pressurized distillation, wherein the top discharge of the atmospheric pressure catalytic distillation tower 1 is extracted at a flow rate of 1962.673 kg / h, and then pumped to the first-stage pressurized distillation tower 2. The water generated by the reaction and the water brought in by the formaldehyde aqueous solution are collected at the bottom of the tower, and as process wastewater, are extracted and discharged from the bottom of the first catalytic distillation tower at a flow rate of 1476.561 kg / h.
[0075] S20, the methylal-methanol blend transported through the first discharge pipe 15, and the methylal-methanol blend transported through the fourth discharge pipe 45, enter the first-stage pressurized distillation tower 2 through the second feed port 210, wherein the flow rate of the methylal-methanol blend transported by the first discharge pipe 15 refers to step S10, and the flow rate of the methylal-methanol blend transported by the fourth discharge pipe 45 refers to step S40. The inner diameter of the first-stage pressurized distillation tower 2 is 800mm, the number of effective plates is 30, the spacing between two adjacent plates is 300mm, the number of plates in the second distillation section 27 is 9, the number of plates in the second separation section 28 is 11, and the number of plates in the second stripping section 29 is 10. The operating pressure of the first-stage pressurized distillation tower 2 is 0.8MPa, the reflux ratio is 2, the top temperature is 110°C, and the bottom temperature is 120°C. After the pressure distillation of the first-stage pressure distillation tower 2, a methylal-methanol azeotrope is generated, and the generated methylal-methanol azeotrope is extracted from the top of the tower, and after condensation, a methylal-methanol blend is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the atmospheric pressure recovery distillation tower 4 through the second discharge pipe 26 for distillation, wherein the top discharge of the first-stage pressure distillation tower 2 is extracted at a flow rate of 1733.505 kg / h, and then pumped to the atmospheric pressure recovery distillation tower 4. The methylal solution generated after the pressure distillation is accumulated at the bottom of the tower, and the methylal solution at the bottom of the tower is extracted at a flow rate of 1788.831 kg / h through the second methylal solution extraction pipe 212, and then transported to the second-stage pressure distillation tower 3.
[0076] S30, the methylal-methanol blend transported through the second methylal solution extraction pipe 212 enters the secondary pressure distillation tower 3 through the third feed port 39, wherein the flow rate of the methylal-methanol blend transported by the second methylal solution extraction pipe 212 is referred to step S20. The inner diameter of the secondary pressure distillation tower 3 is 800mm, the number of effective plates is 35, the spacing between two adjacent plates is 500mm, the number of plates in the third distillation section 37 is 10, the number of plates in the third separation section 38 is 13, and the number of plates in the third stripping section 310 is 12. The operating pressure of the secondary pressure distillation tower 33 is 1.5MPa, the reflux ratio is 2.6, the top temperature is 130°C, and the bottom temperature is 140°C. After the pressure distillation of the secondary pressure distillation tower 3, the generated methylal-methanol azeotrope is extracted from the top of the tower, and after condensation, a methylal-methanol blend is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the atmospheric pressure recovery distillation tower 4 through the third discharge pipe 36 for distillation, wherein the top discharge of the secondary pressure distillation tower 3 is extracted at a flow rate of 7.58 kg / h, and then transported to the atmospheric pressure recovery distillation tower 4. The methylal solution generated after the pressure distillation is collected at the bottom of the tower, and the methylal solution at the bottom of the tower is extracted at a flow rate of 1781.251 kg / h through the third methylal solution extraction pipe 312, and then transported to the dehydrator 313 equipped with a molecular sieve, and the molecular sieve can absorb water to obtain a high-purity methylal product.
[0077] S40, the methylal-methanol blend transported through the second discharge pipe 26, and the methylal-methanol blend transported through the third discharge pipe 36, enter the atmospheric pressure recovery distillation tower 4 through the fourth feed port 411, wherein the flow rate of the methylal-methanol blend transported by the second discharge pipe 26 refers to step S20, and the flow rate of the methylal-methanol blend transported by the third discharge pipe 36 refers to step S30. The inner diameter of the atmospheric pressure recovery distillation tower 4 is 800mm, the number of effective plates is 30, the spacing between two adjacent plates is 350mm, the number of plates in the fourth distillation section 46 is 9, the number of plates in the fourth separation section 47 is 12, and the number of plates in the fourth stripping section 48 is 9. The operating pressure of the atmospheric pressure recovery distillation tower 4 is atmospheric pressure, the reflux ratio is 1.8, the tower top temperature is 43°C, and the tower bottom temperature is 62°C. The distillation of the atmospheric pressure recovery distillation tower 4 generates methylal-methanol azeotrope, which is extracted from the top of the tower, and after condensation, a methylal-methanol blend is formed, part of the methylal-methanol blend is refluxed, and the remaining part of the methylal-methanol blend is pumped to the first-stage pressurized distillation tower 2 through the fourth discharge pipe 45 for distillation, wherein the top discharge of the atmospheric pressure recovery distillation tower 4 is extracted at a flow rate of 1559.663 kg / h, and then transported to the first-stage pressurized distillation tower 2. The methanol solution generated after distillation is accumulated at the bottom of the tower, and the methanol solution at the bottom of the tower is extracted at a flow rate of 181.422 kg / h through the methanol extraction pipe 410, and then transported to the first feed port 111.
[0078] It is measured that in the high-purity methylal product prepared in step S30, the mass fraction of methylal is 99.9995%, and the mass percentages of water and methanol are both less than 10 ppm.
[0079] Example 3
[0080] This embodiment is based on Embodiment 2, and the difference is that in step S10, the number of effective plates of the atmospheric catalytic distillation tower 1 is 70, the number of plates of the first distillation section 16 is 16, the number of plates of the first reaction section 17 is 35, and the number of plates of the first stripping section 18 is 19.
[0081] It is measured that in the high-purity methylal product prepared in step S30, the mass fraction of methylal is 99.9996%, and the mass percentages of water and methanol are both less than 10 ppm.
[0082] Example 4
[0083] This embodiment is based on Embodiment 2, and the difference is that in step S10, the number of effective plates of the atmospheric catalytic distillation tower 1 is 80, the number of plates of the first distillation section 16 is 20, the number of plates of the first reaction section 17 is 30, and the number of plates of the first stripping section 18 is 30.
[0084] It is measured that in the high-purity methylal product prepared in step S30, the mass fraction of methylal is 99.9997%, and the mass percentages of water and methanol are both less than 10 ppm.
[0085] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.
Claims
1. A process for preparing high-purity methylal, characterized in that: The following steps are involved: S10, methanol and formaldehyde aqueous solution are transported to a normal pressure catalytic distillation tower and react to generate methylal, a normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure catalytic distillation tower, and waste water is produced from the bottom of the tower, the normal pressure methylal-methanol azeotrope is condensed to form a normal pressure methylal-methanol blend, part of which is refluxed to the normal pressure catalytic distillation tower, and the rest is transported to a primary pressure distillation tower; S20, the methylal-methanol blend transported to the first-stage pressure distillation tower is operated under pressure, the pressurized methylal-methanol azeotrope is extracted from the top of the first-stage pressure distillation tower, and the methylal solution is extracted from the bottom of the tower, and the methylal solution is transported to the second-stage pressure distillation tower, and the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of it is refluxed to the first-stage pressure distillation tower; S30, the methylal solution transported to the secondary pressure distillation tower is under pressure operation, the pressurized methylal-methanol azeotrope is produced from the top of the secondary pressure distillation tower, and the methylal solution is produced from the bottom of the tower, the methylal solution is dehydrated to obtain high-purity methylal, the pressurized methylal-methanol azeotrope is condensed to form a methylal-methanol blend, and part of it is refluxed to the secondary pressure distillation tower.
2. The process for preparing high-purity methylal according to claim 1, wherein: In the step S10, the atmospheric pressure catalytic distillation tower is a plate tower, and the number of effective plates of the atmospheric pressure catalytic distillation tower is 60 to 100.
3. The process for preparing high-purity methylal according to claim 1, wherein: In the step S10, the top temperature of the atmospheric pressure catalytic distillation tower is 40-50° C., and the bottom temperature is 100-110° C.; In the step S20, the operating pressure of the first-stage pressurized distillation tower is 0.7-1.5 MPa, the tower top temperature is 110-120° C., and the tower bottom temperature is 120-130° C.; In the step S30, the operating pressure of the two-stage pressure distillation tower is 1.0-2.0 MPa, the tower top temperature is 125-150°C, and the tower bottom temperature is 135-160°C.
4. The process for preparing high-purity methylal according to claim 1, wherein: The step S30 further includes the following steps: S40, the remaining part of the methylal-methanol blend in step S20 and step S30 is transported to a normal pressure recovery distillation tower, the normal pressure recovery distillation tower is subjected to normal pressure distillation operation, and the normal pressure methylal-methanol azeotrope is produced from the top of the tower, and the methanol solution is produced from the bottom of the tower. The normal pressure methylal-methanol azeotrope is produced from the top of the normal pressure recovery distillation tower, and is condensed to form a normal pressure methylal-methanol blend, part of which is refluxed to the normal pressure recovery distillation tower, and the rest is transported to the first-level pressurized distillation tower.
5. The process for preparing high-purity methylal according to claim 4, characterized in that: In the step S20, the purity of methylal in the formed methylal-methanol blend is 80-85%; In the step S30, the purity of methylal in the formed methylal-methanol blend is 75-80%.
6. The process for preparing high-purity methylal according to claim 4, characterized in that: In the step S40, the top temperature of the atmospheric pressure recovery distillation tower is 40-45°C, and the bottom temperature is 60-65°C.
7. The process for preparing high-purity methylal according to claim 4, characterized in that: In the step S10 and the step S40, the purity of methylal in the atmospheric pressure methylal-methanol blend is 90-93%.
8. The process for preparing high-purity methylal according to claim 1, characterized in that: In the step S20, the purity of the methylal in the methylal solution extracted from the bottom of the first-stage pressurized distillation tower is ≥99.5%; In the step S30, the purity of methylal in the methylal solution extracted from the bottom of the secondary pressure distillation tower is ≥99.95%, and the purity of methylal in the obtained high-purity methylal is ≥99.999%.
9. The process for preparing high-purity methylal according to claim 1, characterized in that: The reflux ratio of the atmospheric pressure catalytic distillation tower, the first-stage pressurized distillation tower, and the second-stage pressurized distillation tower is 1-5.