Reaction separation system for synthesizing polyoxymethylene dimethyl ether

Abstract

The invention relates to the technical field of chemical production systems, in particular to a reaction separation system for synthesizing polyoxymethylene dimethyl ether. Comprising a dividing wall column, a condensation reflux system, a reboiler 1, a reboiler 2, a product pump, an intermediate raw material pump and a reactor, wherein the dividing wall column comprises a tower top rectifying section, a middle stripping section 1 and a middle stripping section 2, the separation system fully utilizes the critical temperature and low-temperature polymerization of formaldehyde into new formaldehyde substances with different polymerization degrees, and combines the boiling point of a polyoxymethylene dimethyl ether product, so that high-activity formaldehyde and dimers in the product are fully separated, and the separation efficiency is improved. And the mixture is pumped into a reactor to be converted into a target product with better market requirements.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production systems, in particular to a reaction separation system for synthesizing polymethoxy dimethyl ethers. Background Art

[0002] Polyoxymethylene dimethyl ether is a component that can be widely used in clean diesel. It has a cetane number of up to 70, contains no sulfur and no aromatics. It can increase the cetane number of diesel, promote combustion, and significantly reduce the emission of harmful gases in automobile exhaust.

[0003] Due to the excellent performance of polyoxymethylene dimethyl ether, its synthesis process has become a hot research direction at home and abroad. Polyoxymethylene dimethyl ether is produced by the reaction of one or more of methanol or methylal with formaldehyde aqueous solution, trioxymethylene, and polyoxymethylene under the catalytic action of an acidic catalyst. However, the reaction product will decompose under acidic conditions in the presence of water, and the reaction conversion rate is not high. Polyoxymethylene dimethyl ether is a homologue with a degree of polymerization of 2-8. However, the most valuable and more suitable for diesel additives is a homologue of polyoxymethylene dimethyl ether with a degree of polymerization of 3-5. Therefore, the generation of a polyoxymethylene dimethyl ether with a degree of polymerization of 3-5 has become an urgent problem to be solved in enterprise production.

[0004] In the reaction system for the production of polyoxymethylene dimethyl ether with a degree of polymerization of 3-5, when the temperature is high, formaldehyde is very likely to undergo a disproportionation reaction to produce a large amount of formic acid. Formic acid not only corrodes the equipment, but also decomposes the product, bringing great difficulties to the subsequent separation.

[0005] At present, in order to obtain high-quality polyoxymethylene dimethyl ether with a degree of polymerization of 3-5, the existing technology mostly adopts the technology of high-temperature separation of formaldehyde and dimer and methylal with a low degree of polymerization. The intermediate material sprayed and absorbed after vaporization is pumped back to the reactor for further reaction. At this time, the raw materials are continuously vaporized and condensed, which not only increases the equipment investment, but also increases the steam consumption and power consumption, which is not conducive to energy saving and environmental protection.

[0006] In order to solve the above problems and synthesize polyoxymethylene dimethyl ethers mainly with a polymerization degree of 3-5, the present invention provides a reaction separation system for synthesizing polyoxymethylene dimethyl ethers. Summary of the invention

[0007] The object of the present invention is to provide a reaction separation system for synthesizing polyoxymethylene dimethyl ethers to solve the problems raised in the above background technology.

[0008] In order to solve the above technical problems, the present invention provides the following technical solution: a reaction separation system for synthesizing polyoxymethylene dimethyl ether.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A reaction separation system for synthesizing polyoxymethylene dimethyl ethers comprises a bulkhead tower, a condensation reflux system, a reboiler 1, a reboiler 2, a product pump, an intermediate raw material pump, and a reactor; wherein the bulkhead tower comprises a top rectifying section, a middle stripping section 1, and a middle stripping section 2; raw materials are introduced into the middle stripping section 1; the reboiler 1 heats the middle stripping section 1; formaldehyde, M1, and M2 with lower boiling points are vaporized to the top rectifying section; a mixed liquid product enriched with M3 and M4 is collected at the bottom of the middle stripping section 1 and pumped out by a product pump; the reboiler 2 heats the middle stripping section 1; and the mixed liquid product enriched with M3 and M4 is pumped out by a product pump. The distillation section 2 is heated, and the mixed liquid of M2 and formaldehyde is enriched at the bottom of the middle stripping section 2, which is pumped out by the intermediate raw material pump, mixed with the external methylal A, and then introduced into the reactor for reaction to obtain a reaction liquid containing M3 and M4. The reaction liquid containing M3 and M4 is mixed with the raw materials and pumped into the middle stripping section 1 together; after the materials are discharged from the top of the tower, they are separated by a condensation reflux system to obtain a mixed liquid containing the M1 crude product and a mixed liquid containing formaldehyde. The mixed liquid containing formaldehyde is refluxed to the top distillation section of the tower, and the mixed liquid containing the M1 crude product is pumped to the methylal unit;

[0011] The reactor is connected to the outlet of the intermediate raw material pump of the middle stripping section 2, and the middle stripping section 1 is connected to the inlet of the product pump;

[0012] The top gas outlet of the top distillation section is connected to the condenser, and a reflux tank and a reflux pump are arranged in the top distillation section;

[0013] Reboilers are respectively provided in the middle stripping section 2 and the middle stripping section 1 to provide heat for the respective stripping sections.

[0014] More optimally, the condensation reflux system includes a condenser, a reflux tank, and a reflux pump; the top discharge obtains a formaldehyde vaporized mixture, which is then condensed by a condenser, refluxed by a reflux tank, and separated by a reflux pump to obtain a mixed liquid containing the M1 crude product and a mixed liquid containing formaldehyde.

[0015] More optimally, the operating pressure of the reactor is 0.3-0.4Mpa, and the temperature is 80-100°C; the operating pressure of the middle distillation section 1 is 0.13-0.15Mpa, and the temperature is 160-185°C; the operating pressure of the middle distillation section 2 is 0.12-0.14Mpa, and the temperature is 90-110°C; the operating pressure of the top distillation section is 0.1-0.13Mpa, and the temperature is 50-70°C.

[0016] More optimally, the raw material is the reaction liquid after the crude fractionation of polymethoxy dimethyl ether, specifically a mixture of water, methanol, formaldehyde, M1, M2, M3, and M4; the total content of M3 and M4 in the mixed liquid product of M3 and M4 is 98-99wt%; the total content of formaldehyde and M2 in the mixed liquid of M2 and formaldehyde is 90-93wt%; the added methylal is material 006, specifically a mixture of methylal and methanol; the content of crude product M1 in the mixed liquid containing crude product M1 is 55-60wt%.

[0017] More optimally, methylal A is added to the reactor to promote the polymerization of M3 and M4 in the reactor; and methylal B is introduced into the top distillation section to polymerize and generate M2.

[0018] More optimally, the mass ratio of the added methylal B to the formaldehyde in the raw material is (1-2):1; in order to control the increase in water content, the reactor increases the amount of the reaction raw materials in the reaction, prevents the reverse reaction and decomposition of the product, and supplements the added methylal A. The mass ratio of formaldehyde in the mixed solution of the added methylal A and M2 and formaldehyde is (3-4):1, and the mass ratio of the added methylal A to M2 in the raw material is (0.4-0.7):1.

[0019] More optimally, the dividing wall tower includes a dividing wall baffle, which divides the middle stripping section into two parts, namely, the middle stripping section 1 and the middle stripping section 2, and the volume ratio of the middle stripping section 1 to the middle stripping section 2 is 7:3.

[0020] In a more optimized manner, the raw material is introduced into the middle stripping section 1, and the reboiler 1 heats the middle stripping section 1 to 160-185°C, vaporizing the formaldehyde, M1, and M2 with lower boiling points to the top distillation section, and the mixed liquid product enriched with the heavy components M3 and M4 is collected at the bottom of the middle stripping section 1 and pumped out by the product pump; the top distillation section is supplemented with methylal B, and the temperature of the top distillation section is 50-70°C, polymerizing to generate M1 and M2 with higher boiling points, and extruding them to the middle stripping section 2; the reboiler 2 heats the middle stripping section 2 to 90-110°C, vaporizing the low boiling point components, and M2 The mixed liquid with formaldehyde is enriched at the bottom of the middle distillation section 2, pumped out by the intermediate raw material pump, mixed with the added methylal A and then introduced into the reactor for reaction. The temperature of the reactor is controlled at 80-100°C to promote the polymerization of formaldehyde to generate a reaction liquid containing M3 and M4. The reaction liquid containing M3 and M4 is mixed with the raw materials and pumped into the middle distillation section 1. After the material is discharged from the top of the tower, it is separated by a condensation reflux system to obtain a mixed liquid containing the M1 crude product and a material containing formaldehyde. The material containing formaldehyde is refluxed to the top distillation section of the tower, and the mixed liquid containing the M1 crude product is pumped to the methylal unit.

[0021] More optimally, in order to prevent M2 from decomposing into M1 with low polymerization degree and promote the synthesis of M3 from formaldehyde and M2, the height-to-diameter ratio of the reactor is 0.5-1.2, so as to reduce the reaction time and promote the synthesis of M3 from active formaldehyde; in order to promote the reaction of water and methylal and improve the progress of formaldehyde rapid polymerization reaction, cationic resin is added to the reactor in an amount of 100-400Kg / m 3 The cationic resin is a macropore styrene or sulfonic acid resin, which can be purchased from DuPont, Sexis, Zhengguang, Lanxiao Technology, Mingzhu or Kairui Resin, etc.

[0022] More optimally, in order to prevent formaldehyde polymerization, the top distillation section tower plate is a bubble cap tower plate with a higher liquid holding capacity; a structured packing is added in the middle stripping section 1; in order to prevent the liquid from drifting in the middle stripping section 2 with a smaller cross section, a ball ring packing is added in the middle stripping section 2;

[0023] The structured packing is made of 304 or 316l stainless steel;

[0024] The ball ring packing is a 304 stainless steel ball ring with a specification of 25 mm.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] The reaction separation system for synthesizing polyoxymethylene dimethyl ether with a polymerization degree of 3-5 mainly of the present invention avoids the occurrence of formaldehyde condensation polymerization, and sets the original spray absorption function inside the tower. The equipment is compact and reduces the equipment investment. At the same time, the next-door tower efficiently enriches unreacted formaldehyde, fully utilizing the unique physical properties of formaldehyde, not only obtaining high-purity formaldehyde, but also separating more intermediate raw materials while avoiding formaldehyde polymerization, further sending them to the reaction, and obtaining more products.

[0027] The reaction equation involved in this paragraph is as follows:

[0028]

[0029] After the unreacted raw materials are efficiently separated, they participate in the reaction conversion again, which ultimately effectively reduces the steam consumption in production and improves the economic value. This process has the advantages of simple process flow, compact equipment, simple operation and low energy consumption.

[0030] Component description: M1, methylal: CH 3 O-[CH 2 O] 1 -CH 3 , boiling point: 42°C; methanol: CH 3 OH, boiling point: 64°C; formaldehyde monomer: CH 2 O: boiling point: -19°C; M2, dimer: CH 3 O-[CH2 O] 2 -CH 3 , boiling point: 105℃; M3, trimer: CH 3 O-[CH 2 O] 3 -CH 3 , boiling point: 155℃; M4, tetramer: CH 3 O-[CH 2 O] 4 -CH 3 , boiling point: 205℃; methanol-(formaldehyde) n :CH 3 OH-[CH 2 O] n , boiling point: 110-150℃; Methylene glycol: HO-[CH 2 O] 1 -H, boiling point: 70-110°C. Note: Since M4-5 (and deeper polymers) are less in the system and are homologous to M3, the specific contents of M4 and M5 are not counted in the examples, only the total content of M4, M5 or deeper polymers is counted, expressed as M4 content. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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:

[0032] Figure 1 It is a schematic diagram of the structure of the reaction separation system of the present invention;

[0033] In the figure: 1- bulkhead tower; 2- condenser; 3- reflux tank; 4- reflux pump; 5- reboiler 2; 6- reboiler 1; 7- product pump; 8- intermediate raw material pump; 9- reactor; 101- top distillation section; 102- bulkhead baffle; 104- middle stripping section 1; 103- middle stripping section 2;

[0034] 001-raw material; 002-reaction liquid containing M3 and M4; 003-mixture of 001 and 002; 004-mixture product of M3 and M4; 005-mixture of M2 and formaldehyde; 006-added methylal A; 007-added methylal B; 008-formaldehyde vaporized mixture; 009-mixture containing formaldehyde; 010-mixture containing crude product of M1. DETAILED DESCRIPTION

[0035] 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.

[0036] A reaction separation system for synthesizing the polymerization degree of polyoxymethylene dimethyl ether, comprising a bulkhead tower 1, a condenser 2, a reflux tank 3, a reflux pump 4, a reboiler 2 labeled 5, a reboiler 1 labeled 6, a product pump 7, an intermediate raw material pump 8, a reactor 9, a tower top rectifying section 101, a bulkhead baffle 102, a middle stripping section 1 labeled 104, and a middle stripping section 2 labeled 103;

[0037] The next-wall tower 1 is a dividing wall distillation tower with a baffle in the middle, and the reaction liquid 001 after the coarse fractionation of the material polyoxymethylene dimethyl ether is pumped to the middle upper part of the next-wall stripping section 1 labeled 104 on the left side of the next-wall tower 1; a reboiler 1 labeled 6 is arranged at the bottom of the next-wall stripping section 1 labeled 104 on the left side, and the temperature of the reboiler 1 is set to: 160-185°C, and the operating pressure is 0.13-0.15Mpa; through the steam heating effect, the bottom of the next-wall stripping section 1 labeled 104 on the left side obtains a mixed liquid product of M3 and M4 with a polymerization degree of 3-5 having a higher boiling point; trioxymethylene, methylal, and formaldehyde with various polymerization degrees having a lower boiling point are decomposed into monomer formaldehyde through high temperature and vaporized to the top of the tower, so that formaldehyde is effectively separated in the product, thereby obtaining a mixed liquid product of M3 and M4 with a higher purity;

[0038] The high-temperature vaporized formaldehyde is vaporized to the distillation section 101 at the top of the bulkhead tower 1. After the methylal with a lower boiling point added to the top of the tower and the reflux at the top of the tower, the formaldehyde is polymerized again into a high-boiling substance of oligomers. Therefore, under the interaction of the heat in the bottom of the tower and the cooling at the top of the tower, the formaldehyde and other intermediate components with a boiling point of about 50-140° C. are squeezed to the bulkhead stripping section 2 labeled 103.

[0039] A reboiler 2 with a reference number 5 is provided at the bottom of the distillation section 2 with a reference number 103. Through the heating and vaporization action of the reboiler 2, the bottom of the tower gradually enriches dimers and trioxymethylene with relatively high boiling points and formaldehyde with relatively high boiling points and low polymerization degree;

[0040] An intermediate raw material pump 8 is provided at the bottom of the next-door stripping section 2, which is labeled 103, and the materials in the bottom of the tower are pumped to the reactor 9; further, in order to adjust the ratio of the reaction raw materials and prevent overreaction; at the same time, in order to ensure the low content of water in the system, moderately high-purity methylal is added, and the reverse reaction of methylal synthesis is used to further react away part of the water to prevent the generation of formic acid, making the system more reliable and stable;

[0041] Reactor 9 feed components come from intermediate raw material pump 9 and external methylal, respectively. After mixing with each other, a suitable higher reaction temperature is obtained. This temperature is conducive to the hydrolysis reaction of methylal. A higher temperature is conducive to the condensation reaction of dimer and formaldehyde, avoiding the formation of more methylal and formaldehyde due to the full reaction of dimer. This reactor makes full use of high temperature and high activity formaldehyde. Under the acidic conditions where the temperature is reduced and the reaction raw materials exist together, formaldehyde tends to polymerize into a stable substance, and M3-5 is its only polymerization direction.

[0042] The reaction liquid after the reaction is mixed with the crude raw material from the polyoxymethylene dimethyl ether separation unit and then pumped into the dividing wall tower 1 together;

[0043] A condenser 2 is provided at the top of the distillation section 101 of the next-door tower 1. The top temperature of the tower is controlled by controlling the amount of circulating water. Furthermore, a lower top temperature is beneficial for the polymerization of formaldehyde. At the same time, the polymerization of formaldehyde in the liquid phase prevents the polymerization of formaldehyde into high-polymerization degree polyformaldehyde. The dissolving effect of the reaction liquid on the polymerized formaldehyde effectively prevents the unlimited increase of the formaldehyde polymerization chain length. Supplementary methylal is pumped from the top of the tower or together with the reflux line to the top distillation section of the tower.

[0044] Embodiment: A reaction separation system for synthesizing polyoxymethylene dimethyl ether:

[0045] (1) taking a crude reaction liquid of polyoxymethylene dimethyl ether 001 and pumping it to the top third of the distillation section 1 of the next-door tower 1 labeled 104; evaporating it in a reboiler 1 labeled 6 arranged in the bottom of the tower to separate the heavy components, trioxymethylene, methylal, and formaldehydes of various polymerization degrees in the feed components are vaporized to the top of the tower at high temperature, and a mixed liquid product 004 of M3 and M4 with high boiling points is obtained at the bottom of the distillation section 1 of the next-door tower 1, wherein the operating temperature of the reboiler 1 is 170° C. and the operating pressure is 0.15 MPa;

[0046] Table 1 Content of each component of material 001

[0047] 001 water <![CDATA[CH 3 OH]]> M1 formaldehyde M2 M3 M4 Summary Mass / Kg 115.0 450.0 550.0 675.0 1650.0 1010 550 5000 Proportion 2.3％ 9.0％ 11.0％ 13.5％ 33.0％ 20.2％ 11.0％ 100.0％

[0048] Polyoxymethylene dimethyl ether 004, which is mainly of degree of polymerization 3-5, is pumped from product pump 7 to the tank area;

[0049] Table 2 Content of each component of material 004

[0050] 004 water <![CDATA[CH 3 OH]]> M1 formaldehyde M2 M3 M4 Summary Mass / Kg 0 0 0 15.9 44.4 2366.2 684.5 3110.9 Proportion 0.0％ 0.0％ 0.0％ 0.5％ 1.4％ 76.1％ 22.0％ 100.0％

[0051] (2) After vaporization, the relatively low-light components such as trioxymethylene, M2 dimer, and formaldehyde are vaporized to the top of the tower and then condensed and cooled at the top of the tower; substances with relatively high boiling points but far lower than 3-5 polymers are squeezed to the distillation section 2 of the next wall marked 103 under the interaction of the top condensation and the tower kettle heating;

[0052] The reactor of the next-wall stripping section 1 is provided with a reboiler 2 with a reference number of 5. After heating and vaporization in the reboiler 2 and separation in the next-wall stripping section 1, the M2 dimer with a boiling point of 105°C, trioxymethylene with a boiling point of 112-115°C, low-polymerization degree formaldehyde, and hemiacetal are gradually enriched in the reactor of the next-wall stripping section 1. The components are highly active and unstable, and are highly active raw materials for synthesizing trimer M3 and tetramer M4. In this process, the operating temperature of the reactor of the next-wall stripping section 1 is 100°C, the operating pressure is 0.13Mpa, and the mixed liquid of M2 and formaldehyde is extracted by the intermediate raw material pump 8.

[0053] After being vaporized by the reboiler 1 labeled 6, the formaldehyde is vaporized into monomer formaldehyde with a lower boiling point and a higher activity, and then vaporized to the distillation section 101 at the top of the dividing wall tower 1. At this time, the top of the tower is supplemented with 42°C methylal with a boiling point. Due to the methylal with a lower boiling point supplemented at the top of the tower and the reflux at the top of the tower, the formaldehyde is cooled and polymerized again into a low-polymer high-boiling-point substance;

[0054] Under the interaction of the heat in the tower bottom and the cooling at the top of the tower, formaldehyde and components with a boiling point of about 50-140°C are squeezed to the dividing wall stripping section 2 labeled 103;

[0055] Table 3 Content of each component of material 005

[0056] 005 water <![CDATA[CH 3 OH]]> M1 formaldehyde M2 M3 M4 Summary Mass / Kg 98.8 23.2 37.5 455.7 2297.7 84.1 3.2 3000.0 Proportion 3.3％ 0.8％ 1.2％ 15.2％ 76.6％ 2.8％ 0.1％ 100.0％

[0057] (3) The bottom of the next-door stripping section 2 labeled 103 is provided with an intermediate raw material pump 8, and the mixed liquid 005 of M2 and formaldehyde is pumped into the reactor 9 through the raw material pump 8, and the methylal A006 is added to supplement, so as to control the reaction to better proceed to the target of polymerization of m3-5;

[0058] Table 4 Content of each component of methylal 006

[0059] 006 <![CDATA[CH 3 OH]]> M1 Summary Mass / Kg 90.0 1410.0 1500 Proportion 6.0％ 94.0％ 100.0％

[0060] The preferred operating temperature of the reactor 9 is controlled to be 90°C, and the operating pressure is 0.35Mpa. The reactor is filled with solid acid. To prevent excessive pressure drop, a filler layer can be added in the middle or a radial reactor can be selected. After conversion in the reactor 9, a reaction liquid 002 containing M3 and M4 is obtained. A portion of water is consumed by the reaction with methylal. At the same time, after passing through the reactor, formaldehyde is greatly converted, and the measured conversion rate reaches 77%. The content of dimer M2 is relatively large. Under a relatively high temperature operating environment, a large amount of formaldehyde rapidly decomposed from dimer M2 synthesizes a more stable m3-5 with excess methylal. After the reaction, a reaction liquid 002 containing M3 and M4 is obtained, which is mixed with raw material 001 and pumped into the next-door tower 1.

[0061] Table 5 Content of each component of material 002

[0062]

[0063] (4) The liquid portion after evaporation and condensation at the top of the dividing tower 1 is used for reflux of the mixed liquid 009 containing formaldehyde, and the mixed liquid 010 containing the crude product M1 with low aldehyde and high alcohol content is pumped to the methylal unit for further treatment, and the top of the tower is supplemented with methylal B 007, which can be methylal with a purity of 85-94%;

[0064] Table 6 Content of each component of material 007

[0065] 007 <![CDATA[CH 3 OH]]> M1 Summary Mass / Kg 72.0 1128.0 1200 Proportion 6.0％ 94.0％ 100.0％

[0066] The additional methylal B 007 is used to control the tower top temperature, so as to promote the polymerization of formaldehyde into a high-boiling polymer at low temperature and reduce the amount of formaldehyde overflowing from the tower top. The mass ratio of the supplementary amount of methylal to the formaldehyde in the raw material 001 is 1.5:1. In this embodiment, it can be seen that the mass of methylal is 1128kg, the formaldehyde content of the feed is 675kg, and the ratio is 1.67 in the experiment. Under this ratio, the tower top temperature is well controlled and the overflow of formaldehyde from the tower top is prevented.

[0067] By controlling a reasonable reflux ratio, the optimal operating temperature at the top of the tower is 60°C and the operating pressure is 0.12Mpa;

[0068] Table 7 Content of each component of material 010

[0069] 010 water <![CDATA[CH 3 OH]]> M1 formaldehyde M2 M3 M4 Summary Mass / Kg 105.13 647.15 2857.42 58.26 532.03 0.00 0.00 4200.00 Proportion 2.1％ 12.9％ 57.1％ 1.2％ 10.6％ 0.0％ 0.0％ 84.0％

[0070] Since dimer M2 has a certain azeotropic property with water, and the azeotropic point is about 80°C, a certain amount of dimer M2 is lost at the top of the tower, and at the same time, the water that may be enriched in the system is effectively removed, preventing the formation of formic acid; the reflux ratio of the adjacent tower 1 is controlled to be 1.5:1, so as to control the top temperature of the tower to be no higher than 70°C, prevent formaldehyde from overflowing, and increase the temperature to facilitate the extraction of water from the top of the tower in the form of azeotropy;

[0071] Comprehensive comparison shows that feed components directly affect separation and reaction. In order to prevent formaldehyde polymerization and efficient reaction, it is crucial to select the appropriate amount of methylal supplementation. The amount of methylal supplementation at the top of the tower is closely related to the feed formaldehyde concentration. The reaction effect of the reactor and the water content in the system are also affected by the supplementary methylal. The appropriate amount of methylal supplementation makes the operation more flexible. After multiple experimental verifications, it has been proved that the system operation control and flexibility are highly feasible, which further proves the feasibility of the process.

[0072] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether, characterized in that: The invention comprises a dividing wall tower (1), a condensation reflux system, a reboiler 1 (6), a reboiler 2 (5), a product pump (7), an intermediate raw material pump (8), and a reactor (9); wherein the dividing wall tower (1) comprises a tower top rectifying section (101), a middle stripping section 1 (104), and a middle stripping section 2 (103); the raw material (001) is introduced into the middle stripping section 1 (104); the reboiler 1 (6) heats the middle stripping section 1 (104); formaldehyde, M1, and M2 with lower boiling points are vaporized to the tower top rectifying section (101); a mixed liquid product (004) enriched with M3 and M4 is collected at the bottom of the middle stripping section 1 (104) and pumped out by a product pump (7); The reboiler 2 (5) heats the middle stripping section 2 (103), and a mixed liquid (005) enriched with M2 and formaldehyde is collected at the bottom of the middle stripping section 2 (103), which is pumped out by an intermediate raw material pump (8), mixed with external methylal A (006), and then introduced into a reactor (9) for reaction to obtain a reaction liquid (002) containing M3 and M4. The reaction liquid (002) containing M3 and M4 is mixed with the raw material (001) and pumped into the middle stripping section 1 (104). After the material is discharged from the top of the tower, it is separated by a condensation reflux system to obtain a mixed liquid containing a crude product mainly composed of M1, part of which (009) participates in reflux, and part (010) is pumped to the methylal unit.

2. A reaction separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: The condensation reflux system comprises a condenser (2), a reflux tank (3), and a reflux pump (4); the top discharge obtains a formaldehyde vaporized mixture (008), which is then condensed by the condenser (2), refluxed by the reflux tank (3), and separated by the reflux pump (4) to obtain a mixed liquid (010) containing a crude M1 product and a mixed liquid (009) containing formaldehyde.

3. A reaction separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: The operating pressure of the reactor (9) is 0.3-0.4Mpa and the temperature is 80-100°C; the operating pressure of the middle stripping section 1 (104) is 0.13-0.15Mpa and the temperature is 160-185°C; the operating pressure of the middle stripping section 2 (103) is 0.12-0.14Mpa and the temperature is 90-110°C; the operating pressure of the top distillation section (101) is 0.1-0.13Mpa and the temperature is 50-70°C.

4. A reaction separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: The raw material (001) is the reaction liquid after the coarse fractionation of polyoxymethylene dimethyl ether, specifically a mixture of water, methanol, formaldehyde, M1, M2, M3, and M4; the total content of M3 and M4 in the mixed liquid product (004) of M3 and M4 is 98-99wt%; the total content of formaldehyde and M2 in the mixed liquid (005) of M2 and formaldehyde is 90-93wt%; the added methylal is material 006, specifically a mixture of methylal and methanol; the content of crude product M1 in the mixed liquid (010) containing the crude product M1 is 55-60wt%.

5. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: Methylal A (006) is added to the reactor to promote the polymerization of M3 and M4 in the reactor; and methylal B (007) is introduced into the top distillation section (101) to polymerize and generate M2.

6. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 5, characterized in that: The mass ratio of the added methylal B (007) to the formaldehyde in the raw material (001) is (1-2):1; the mass ratio of the added methylal A (006) to the formaldehyde in the mixed solution (005) of M2 and formaldehyde is (3-4):1, and the mass ratio of the added methylal A (006) to M2 in the raw material (001) is (0.4-0.7):

1.

7. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: The dividing wall tower (1) comprises a dividing wall baffle (102), and the dividing wall baffle (102) divides the middle stripping section into two parts, namely, the middle stripping section 1 (104) and the middle stripping section 2 (103), and the volume ratio of the middle stripping section 1 (104) to the middle stripping section 2 (103) is 7:

3.

8. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 1, characterized in that: The raw material (001) is introduced into the middle stripping section 1 (104), and the reboiler 1 (6) heats the middle stripping section 1 (104) to 160-185°C, vaporizes the formaldehyde, M1 and M2 with lower boiling points to the top distillation section (101), and the mixed liquid product (004) enriched with heavy components M3 and M4 is collected at the bottom of the middle stripping section 1 (104) and pumped out by the product pump (7); the top distillation section (101) is supplemented with methylal B (007), and the temperature of the top distillation section (101) is 50-70°C, polymerizes to generate M1 and M2 with higher boiling points, and squeezes them into the middle stripping section 2; the reboiler 2 (5) heats the middle stripping section 2 (103) to 90-110°C, vaporizes the low boiling point components, and the mixed liquid product (004) of M2 and formaldehyde is concentrated to the bottom of the middle stripping section 1 (104). The combined liquid (005) is enriched at the bottom of the middle stripping section 2 (103), pumped out by the intermediate raw material pump (8), mixed with the external methylal A (006), and then introduced into the reactor (9) for reaction. The temperature of the reactor (9) is controlled to be 80-100°C to promote the polymerization of formaldehyde to generate a reaction liquid (002) containing M3 and M4. The reaction liquid (002) containing M3 and M4 is mixed with the raw material (001) and pumped into the middle stripping section 1 (104). After the material is discharged from the top of the tower, it is separated by a condensation reflux system to obtain a mixed liquid (010) containing the M1 crude product and a material (009) containing formaldehyde. The material (009) containing formaldehyde is refluxed to the top distillation section of the tower, and the mixed liquid (010) containing the M1 crude product is pumped to the methylal unit.

9. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 8, characterized in that: The reactor (9) has a height-to-diameter ratio of 0.5-1.2; a cationic resin is added to the reactor (9) in an amount of 100-400 Kg / m 3 .

10. A reaction and separation system for synthesizing polyoxymethylene dimethyl ether according to claim 8, characterized in that: The tower plates of the top distillation section (101) are bubble cap tower plates; regular packing is added in the middle stripping section 1 (104); and ball ring packing is added in the middle stripping section 2 (103).

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