Refining process for byproduct trioxymethylene of polyoxymethylene dimethyl ether

Abstract

The invention relates to a refining process for a polymethoxy dimethyl ether byproduct trioxymethylene. The refining process comprises a light component removal tower unit process, a vacuum tower unit process and a pressurizing tower unit process, a first condensation cooling reflux system, a circulating cooling spray absorption system and a second condensation cooling reflux system are respectively arranged in each unit process for rectification separation, and the steam consumption is reduced through azeotropic dehydration on the premise of accurately utilizing the physical property of formaldehyde and realizing non-polymerization of the formaldehyde; the method has the advantages that the production of formic acid is prevented through vacuum low-temperature dehydration, high-activity hemiacetal is reserved in a polyoxymethylene dimethyl ether system to continuously participate in the raw material reaction, and trioxymethylene in the reaction liquid during polyoxymethylene dimethyl ether synthesis is obtained through separation, so that the product diversification of enterprises is greatly increased, and the economic benefit is improved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production processes, in particular to a refining process for by-product trioxymethylene from polyoxymethylene dimethyl ether. Background Art

[0002] Trioxane, also known as trioxane, trimethoxy aldehyde, 1,3,5-trioxane, is an organic compound with the chemical formula C 3 H 6 O 3 . White crystals, melting point 64℃, boiling point 114.5℃. Sublimes at 46℃. Soluble in water, alcohol, ether, acetone, chloroform, carbon disulfide, aromatic hydrocarbons and other organic solvents, slightly soluble in petroleum ether and pentane.

[0003] The synthesis method of trioxymethylene can be classified into liquid sulfuric acid process and solid acid process according to the synthesis catalyst. Sulfuric acid process: 37-40% industrial formaldehyde is concentrated to 60-70%, and trioxymethylene is synthesized at 100°C in the presence of concentrated sulfuric acid. This process has the inevitable disadvantages of homogeneous catalysis itself, such as easy corrosion of equipment, poor selectivity, and difficulty in separating products from catalysts. The reaction equilibrium constant is small, and only trioxymethylene with an equilibrium composition of about 3% is obtained in the reaction liquid. Solid acid process: Use cation exchange resin to catalyze formaldehyde aqueous solution to obtain a balanced solution of trioxymethylene, formaldehyde and water. Add appropriate solvent to separate trioxymethylene from the balanced solution in the extractor, reduce the concentration of trioxymethylene in the reaction solution, and make the subsequent reaction move towards the direction of generating trioxymethylene. Compared with the sulfuric acid process, the introduction of the extractant increases the conversion rate to a certain extent. The solvent used in the extraction unit is a halogenated aliphatic hydrocarbon or a halogenated aromatic hydrocarbon. The extraction separation technology needs to recycle the solvent for extraction and distillation, which will inevitably consume a lot of energy. At the same time, since the extraction solvents used (mostly benzene or its homologues) are often dangerous and harmful substances, they will inevitably cause pollution to the environment.

[0004] At the same time, a large amount of dilute aldehyde will be produced during the preparation of trioxymethylene. The dilute aldehyde has low application quality and can only be used to synthesize methylal or urotropine with relatively saturated market capacity and low economic value.

[0005] During the synthesis of polyoxymethylene dimethyl ether, considerable trioxymethylene is also generated under acidic conditions with high aldehyde content, and the presence of trioxymethylene affects the product quality of polyoxymethylene dimethyl ether to a certain extent. At the same time, dilute formaldehyde is the raw material for synthesizing methylal, and methylal is the raw material for synthesizing polyoxymethylene dimethyl ether, so there is no by-product of dilute formaldehyde.

[0006] In order to prepare high-quality trioxymethylene, the present invention makes full use of the physical properties of formaldehyde and separates trioxymethylene with higher economic value from the polyoxymethylene dimethyl ether reaction liquid, which not only improves the product purity of the polyoxymethylene dimethyl ether, increases the diversification of the enterprise's products, greatly reduces energy consumption, reduces the requirements of the acidic environment on equipment, but also improves the operating profit of the enterprise. Summary of the invention

[0007] The object of the present invention is to provide a purification process for trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether, which is refined and purified according to the difference in azeotropic points of a mixture of components in a reaction solution in proportion, so as to solve the problems raised in the above background technology.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A refining process for trioxymethylene as a byproduct of polyoxymethylene dimethyl ether, specifically comprising: a lightness removal tower unit process, a vacuum tower unit process, and a pressure tower unit process; the specific flow of each process is as follows:

[0010] S1: Lightness Removal Tower Unit Process:

[0011] The reaction liquid after the coarse fractionation of polyoxymethylene dimethyl ether is pumped into a light-removal tower for the first distillation separation: a removal gas A is produced at the top of the light-removal tower, and a reaction liquid A is obtained in the bottom of the light-removal tower;

[0012] S2: Vacuum tower unit process:

[0013] The reaction liquid A is pumped into a vacuum tower through a discharge pump of the tower kettle of the light-removing tower at one end of the bottom of the light-removing tower, and is evacuated to vacuum through the vacuum pump. After the gas is discharged, a second distillation separation is performed: a mixed liquid containing polyoxymethylene dimethyl ether and hemiacetal is discharged from the discharge pump of the tower kettle of the vacuum tower at one end of the bottom of the vacuum tower, and a mixed gas is discharged from the top of the vacuum tower; wherein the mixed gas is liquefied and enriched through a vacuum spray tank to obtain a low-aldehyde material; wherein the low-aldehyde material includes: a first part of low-aldehyde material, a second part of low-aldehyde material, and a third part of low-aldehyde material;

[0014] S3: Pressurized tower unit process:

[0015] The third part of low-aldehyde material is pumped into the pressure tower through the vacuum tower reflux pump for the third distillation separation: the top of the pressure tower produces a removal gas B, and the pressure tower kettle discharge pump at one end of the bottom of the pressure tower discharges the material to obtain the refined trioxymethylene.

[0016] The reaction equation involved in this refining process is as follows:

[0017]

[0018]

[0019] Component description: M1 methylal: CH 3 O-[CH 2 O] 1 -CH 3 , boiling point: 42℃; formaldehyde: CH 2 O, boiling point: 64°C; M2 dimer: CH 3 O-[CH 2 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℃; trioxymethylene: [CH 2 O] 3 , boiling point: 114℃; Methylene glycol: HO-CH 2 OH; Polymerization degree formaldehyde: HO-[CH 2 O] n -H; hemiacetal: CH 3 O-[CH 2 O] n -H, n=1-3.

[0020] The present invention is based on the difference in azeotropic points of the mixture of components in the reaction solution in proportion to perform refining and purification. The azeotropic description of the relevant components is as follows:

[0021] Azeotrope of trioxymethylene and water in a volume ratio of 70:30, azeotropic temperature: 91.4°C;

[0022] The dimer M2 and water form an azeotrope with a volume ratio of 80:20, and the azeotropic temperature is 80.9°C;

[0023] The azeotrope of methylal, methanol and water in a volume ratio of 93:6.5:0.5 has an azeotropic temperature of 42.4°C.

[0024] The azeotrope of trioxymethylene, formaldehyde and water in a volume ratio of 69:5:26 has an azeotropic temperature of 70-90°C.

[0025] More optimally, a light-removal tower reboiler is provided at the other end of the bottom of the light-removal tower; a vacuum tower reboiler is provided at the other end of the bottom of the vacuum tower; and a pressure tower reboiler is provided at the other end of the bottom of the pressure tower.

[0026] More optimally, the light removal tower, vacuum tower and pressure tower all use bubble cap or float valve trays.

[0027] The use of bubble cap or float valve plates can increase the liquid holding capacity between plates and prevent formaldehyde polymerization from clogging the pipeline due to dry plates.

[0028] More optimally, in the light removal tower unit process, a first condensation cooling reflux system is set at the top of the light removal tower to treat the removed gas A; the treatment method is: the removed gas A is sequentially treated by the light removal tower condenser, the light removal tower reflux tank, and the light removal tower reflux pump to obtain a removed component A; wherein the removed component A includes: a first removed component A and a second removed component A; the first removed component A continues to participate in the reflux reaction at the top of the light removal tower, and the second removed component A is pumped to the methylal reaction unit to further synthesize methylal.

[0029] More optimally, in the vacuum tower unit process, a circulating cooling spray absorption system is set at the top of the vacuum tower to treat the mixed gas; the treatment method is: the mixed gas is condensed and absorbed by a vacuum spray tank to obtain a low-aldehyde material; wherein, the first part of the low-aldehyde material is sequentially treated by a vacuum tower reflux pump and a vacuum cooler for reflux reaction in the vacuum tower spray tank; the second part of the low-aldehyde material is pumped into the vacuum tower through the vacuum tower reflux pump to participate in the reflux reaction at the top of the vacuum tower; the third part of the low-aldehyde material is pumped into the pressurized tower through the vacuum tower reflux pump to continue the third distillation separation; the material that is not absorbed is discharged through the vacuum pump.

[0030] More optimally, the vacuum tower spray tank uses bulk filler ball rings that are easy to load and unload.

[0031] More optimally, the connection method of the various equipment in the circulating cooling spray absorption system is as follows: the top of the vacuum tower is connected to the space above the bottom liquid level of the vacuum tower spray tank through a gas phase pipeline, and the gas phase is evenly distributed in the form of a row pipe; the inlet of the vacuum tower cooler is connected to the outlet of the vacuum tower reflux pump; the outlet of the vacuum tower cooler is connected to the space above the packing section at the top of the vacuum tower spray tank, and the liquid phase is evenly distributed in the form of a row pipe; the inlet of the vacuum pump is connected to the gas phase space at the top of the vacuum tower spray tank.

[0032] More optimally, in the pressurized tower unit process, a second condensation cooling reflux system is set at the top of the pressurized tower to treat the removed gas B; the treatment method is: the removed gas B passes through the pressurized tower condenser, the pressurized tower reflux tank, and the pressurized tower reflux pump in sequence to obtain a removed component B; wherein the removed component B includes: a first removed component B and a second removed component B; the first removed component B continues to participate in the pressurized tower top reflux reaction, and the second removed component B is added to the polyoxymethylene dimethyl ether reaction system.

[0033] Since the top of the light-removal tower contains a large amount of water and methanol, formaldehyde polymerization and blockage will not occur during the condensation and cooling process of the top of the tower, so the condenser of the light-removal tower is preferably a shell-and-tube cooler; the vacuum tower adopts a circulating cooling spray absorption process to prevent the overflow of free formaldehyde from gasifying to the top condenser and causing formaldehyde polymerization to block the condenser; there is a large amount of dimer M2 with good solubility at the top of the pressurized tower, and the formaldehyde content is relatively low. Under high temperature conditions, there is no formaldehyde polymerization and blockage of the pipeline. Therefore, in order to increase the condensation cooling effect and reduce the flow of the spray pump, a conventional condensation cooling system is selected for the top of the pressurized tower.

[0034] More optimally, in S1, the first distillation separation condition is: under normal pressure, the temperature at the top of the lightness removal tower is 50-80°C.

[0035] More optimally, the temperature at the top of the lightness removal tower is 50-70°C.

[0036] In the scheme, after the reaction liquid after the coarse separation of polyoxymethylene dimethyl ether in S1 is pumped into the middle upper part of the light-removing tower, in order to reduce the energy consumption of evaporating water and prevent formaldehyde from undergoing disproportionation reaction with water in the system, distillation separation is carried out under a normal pressure and relatively low temperature working environment; since methylal, methanol and water can form an azeotrope in a ratio of 93:6.5:0.5 with an azeotropic temperature of 42.4°C, and trioxymethylene, formaldehyde and water can form an azeotrope in a ratio of 69:5:26 with an azeotropic temperature of 70-90°C, in the scheme, distillation separation is carried out based on the principle of the azeotropic properties of dimer M2 and water and trioxymethylene and water, so as to remove light components such as methylal, free methanol, free formaldehyde, water and its azeotropic mixture formed with trioxymethylene and dimer M2 in the reaction liquid, so as to reduce the load of the vacuum tower, and finally obtain a reaction liquid A mainly composed of polyoxymethylene dimethyl ether, hemiacetal and trioxymethylene in the tower kettle of the light-removing tower.

[0037] More optimally, in S2, the second distillation separation conditions are: the temperature at the top of the vacuum tower is 60-70°C; the pressure at the bottom of the vacuum tower is 0.03-0.06MPa, and the temperature is 80-95°C.

[0038] Since the ratio of triformaldehyde and water is 70:30, the azeotropic mixture has an azeotropic temperature of 91.4°C; the ratio of dimer M2 and water is 80:20, the azeotropic mixture has an azeotropic temperature of 80.9°C. Therefore, in the scheme, after secondary distillation separation, the temperature is increased, so that the mixed gas formed by triformaldehyde and dimer M2 with relatively low boiling points is extracted from the top of the vacuum tower, and then sprayed by circulating cooling in the vacuum tower spray tank and the vacuum tower cooler to liquefy and enrich the gas to obtain low-aldehyde materials; part of the low-aldehyde materials participate in the reflux of the vacuum tower to speed up the refining speed. , the remaining part is pumped into the pressure tower through the vacuum tower reflux pump; the polyoxymethylene dimethyl ether and hemiacetal with relatively high boiling points are left in the vacuum tower kettle, but in order to prevent the decomposition of hemiacetal, the tower kettle temperature should not be too high to prevent it from decomposing into formaldehyde and overflowing from the tower top, and allowing high-boiling point substances to enter the pressure tower, and ensuring that the pressure tower will not react with water due to the large formaldehyde content to produce a large amount of formic acid, affecting the subsequent trioxymethylene purification; the materials in the tower kettle are then pumped to the polyoxymethylene dimethyl ether refining unit through the vacuum tower kettle discharge pump to continue to participate in purification or reaction.

[0039] More optimally, in S3, the third distillation separation conditions are: the pressure of the pressure tower kettle is 0.25-0.45 MPa, and the temperature is 130-155°C; the pressure of the pressure tower top is 0.20-0.40 MPa, and the temperature is 100-120°C.

[0040] In order to better improve the purity of triformaldehyde in the kettle of the pressure tower and remove impurities, the low-aldehyde material is pumped into the pressure tower by utilizing the property that hemiacetal can easily decompose into formaldehyde and methanol at high temperature. After pressurization and temperature increase in the pressure tower, a small amount of unstable low-polymer formaldehyde is decomposed into methanol, formaldehyde or free state, and then completely vaporized to the top of the pressure tower. Water and dimer M2 with similar boiling points are discharged from the top of the pressure tower with azeotropy. After condensation and cooling, they are dissolved in dimer M2 in the form of polyformaldehyde and are pumped into the polyoxymethylene dimethyl ether reaction system for repeated reaction. The pressurization in the kettle of the pressure tower destroys the azeotropic composition of triformaldehyde and water, and the kettle can collect the refined and purified triformaldehyde.

[0041] Beneficial effects of the invention: The invention provides a purification process for trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether, which separates trioxymethylene synthesized from polyoxymethylene dimethyl ether, improves the purity of the polyoxymethylene dimethyl ether product, increases the product diversification of the enterprise, and improves the economic benefits. The process has the advantages of simple process flow, compact equipment, simple operation, low energy consumption, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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:

[0043] Figure 1 It is a specific refining process flow chart of the present invention;

[0044] In the attached figure: 1: lightness removal tower, 2: lightness removal tower condenser, 3: lightness removal tower reflux tank, 4: lightness removal tower reflux pump, 5: lightness removal tower reboiler, 6: lightness removal tower kettle discharge pump, 7: vacuum tower, 8: vacuum tower reboiler, 9: vacuum tower kettle discharge pump, 10: vacuum tower spray tank, 11: vacuum pump, 12: vacuum tower cooler, 13: vacuum tower reflux pump, 14: pressurizing tower, 15: pressurizing tower condenser, 16: pressurizing tower reflux tank, 17: pressurizing tower reflux pump, 18: pressurizing tower reboiler, 19: pressurizing tower kettle discharge pump;

[0045] 001: reaction liquid after coarse fractionation of polyoxymethylene dimethyl ether; 002: first removed component A; 003: second removed component A; 004: reaction liquid A; 005: mixed liquid B; 006: mixed gas of trioxymethylene and dimer M2; 007: material not absorbed by the circulating cooling spray absorption process; 008: first part of low-aldehyde material; 009: second part of low-aldehyde material; 010: third part of low-aldehyde material; 011: first removed component B; 012: second removed component B; 013: refined trioxymethylene. DETAILED DESCRIPTION

[0046] 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.

[0047] A refining process for trioxymethylene as a byproduct of polyoxymethylene dimethyl ether, the specific refining process flow is as follows:

[0048] S1: Lightness removal tower unit process: the reaction liquid 001 after the coarse fractionation of polyoxymethylene dimethyl ether is pumped into the middle upper part of the lightness removal tower 1, the temperature of the top of the lightness removal tower 1 is controlled to be 50-55°C, and the light components with relatively low boiling points in the feed components, such as methylal, free methanol, free formaldehyde, water and the azeotrope formed with trioxymethylene and dimer M2, are removed, and the light components are gasified to the top of the lightness removal tower 1 to obtain a removal gas A, and the removal gas A is cooled by a shell-and-tube cooler to obtain a removal component A; wherein the first removal component A002 continues to participate in the reflux reaction at the top of the lightness removal tower 1, and the second removal component A003 is pumped to the methylal unit to further synthesize methylal, so as to continue to participate in the synthesis reaction; finally, a reaction liquid A004 mainly composed of polyoxymethylene dimethyl ether, hemiacetal and trioxymethylene is obtained in the bottom of the lightness removal tower 1;

[0049] S2: Vacuum tower unit process: The reaction liquid A004 is pumped into the lower middle part of the vacuum tower 7 through the discharge pump 6 of the tower kettle of the light removal tower 1, and the vacuum tower 7 is evacuated by the vacuum pump 11 to make the materials distilled and separated at a relatively low pressure, and at the same time, the temperature at the top of the vacuum tower 7 is controlled to be 65±3°C; the pressure of the tower kettle of the vacuum tower 7 is 0.04MPa, and the temperature is 85±3°C; the component 005 with a larger boiling point is left in the tower kettle of the vacuum tower 7, and then pumped to the polyoxymethylene dimethyl ether refining unit through the discharge pump 9 of the tower kettle of the vacuum tower 7 to continue to participate in purification or reaction; the mixed gas 006 of trioxymethylene and dimer M2 with a lower boiling point is extracted from the top of the vacuum tower 7, and is treated by a circulating cooling spray absorption system to liquefy and enrich the mixed gas 006 to obtain a low-aldehyde material; the first part of the low-aldehyde material 008 is sequentially treated by a vacuum tower reflux pump 13 and a vacuum cooler 12, and is used for a reflux reaction in a vacuum tower spray tank 10 to accelerate the enrichment rate; the second part of the low-aldehyde material 009 is pumped into the vacuum tower by a vacuum tower reflux pump 13 to participate in the reflux reaction at the top of the vacuum tower 7;

[0050] S3: Pressurized tower unit process: The third part of low-formaldehyde material 010 is pumped into the pressurized tower 14 through the vacuum reflux pump 13; after pressurization and temperature increase, the pressure of the bottom of the pressurized tower 14 is 0.35MPa, and the temperature is 135±3℃; the pressure at the top of the pressurized tower 14 is 0.30MPa, and the temperature is 110±3℃, so that a small amount of unstable low-polymerized formaldehyde is decomposed into layer methanol, formaldehyde or free state, and is completely vaporized to the top of the tower and discharged, and after condensation and cooling, it is dissolved in the dimer M2 in the form of polyformaldehyde, and pumped to the polyoxymethylene dimethyl ether reaction system, and the pressurization in the pressure kettle destroys the azeotropic composition of tripolyformaldehyde and water, thereby making it easier to obtain high-purity tripolyformaldehyde 013 from the bottom of the pressure tower.

[0051] Embodiment: A purification process for trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether:

[0052] (1) taking the reaction liquid 001 (material 001) after the coarse fractionation of polyoxymethylene dimethyl ether, pumping it to the middle upper part of the lightness removal tower 1, heating the lightness removal tower to vaporize the light substances with relatively low boiling points to the top of the lightness removal tower, cooling and removing them through a shell-and-tube cooler, wherein the temperature of the top of the lightness removal tower is 50-55° C.; the first removed component A002 participates in the reflux reaction at the top of the lightness removal tower, and the second removed part A003 (material 003) is pumped to the methylal unit to further synthesize methylal, so as to continue to participate in the synthesis reaction; and a reaction liquid A004 mainly composed of polyoxymethylene dimethyl ether, hemiacetal and trioxymethylene is obtained in the kettle of the lightness removal tower;

[0053] Table 1 Content of each component of material 001

[0054]

[0055] Table 2 Content of each component of material 003

[0056]

[0057] (2) The reaction liquid A004 (material 004) is pumped into the lower middle part of the vacuum tower 7 through the discharge pump 6 of the light removal tower kettle, and the vacuum is evacuated and decompressed by the vacuum pump 11, and then the temperature is increased for distillation separation, wherein the temperature at the top of the vacuum tower 7 is 65±3° C., the pressure in the kettle of the vacuum tower 7 is 0.04 MPa, and the temperature is 85±3° C.; the mixed liquid 005 (material 005) with a relatively high boiling point in the kettle is pumped to the polyoxymethylene dimethyl ether refining unit through the discharge pump 9 of the vacuum tower kettle to continue the reaction;

[0058] Table 3 Content of each component of material 004

[0059]

[0060] Table 4 Content of each component of material 005

[0061]

[0062] (3) A mixed gas 006 of trioxymethylene and dimer M2 with relatively low boiling points is extracted from the top of vacuum tower 07, and the mixed gas 006 is liquefied and enriched to obtain a low-aldehyde material, which is cooled in the form of spraying to absorb free formaldehyde, and the light components that are not absorbed are sent to the tail gas treatment system by the vacuum pump 11 for further absorption and capture; the first part of the low-aldehyde material 008 is sequentially used for the reflux reaction in the vacuum tower spray tank through the vacuum tower reflux pump and the vacuum cooler to accelerate the enrichment speed; the second part of the low-aldehyde material 009 participates in the vacuum tower reflux reaction to accelerate the reaction speed; the third part of the low-aldehyde material 010 (material 010) is pumped into the pressurizing tower 14 through the vacuum tower reflux pump 13;

[0063] Table 5 Content of each component of material 010

[0064]

[0065] (4) The pressure tower 14 is pressurized and the temperature is increased. The pressure in the bottom of the pressure tower is 0.35 MPa and the temperature is 135±3°C. The pressure at the top of the pressure tower is 0.30 MPa and the temperature is 110±3°C. This allows a small amount of unstable oligomeric formaldehyde to decompose into methanol, formaldehyde or free form, which is completely vaporized to the top of the pressure tower. Water and dimer M2, which have similar boiling points, are azeotropically discharged from the top of the pressure tower. After condensation and cooling, they are dissolved in the dimer M2 in the form of polyformaldehyde, which is then pumped into the polyoxymethylene dimethyl ether reaction system. High-quality tripolyformaldehyde 013 (material 013) is collected in the bottom of the pressure tower 14.

[0066] Table 6 Content of each component of material 013

[0067]

[0068] Result analysis: The present invention aims at the physical properties of each component in the reaction liquid after the coarse separation of polyoxymethylene dimethyl ether, and utilizes the characteristics of trioxymethylene that it is easy to decompose at high temperature and is a substance with a higher boiling point at low temperature, and the unique existence form of formaldehyde in the polyoxymethylene dimethyl ether reaction liquid is mostly hemiacetal. Through azeotropic dehydration, steam consumption is reduced; vacuum low-temperature dehydration prevents the formation of formic acid, separates a large amount of formaldehyde from water in the reaction liquid, and thus obtains trioxymethylene with high purity. The present invention greatly increases the product diversification of the enterprise and improves the economic benefits.

[0069] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0070] 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 process for refining trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether, characterized in that: The refining process includes the following steps: a lightness removal tower unit step, a vacuum tower unit step, and a pressure tower unit step; the specific flow of each step is as follows: S1: Lightness Removal Tower Unit Process: The reaction liquid (001) after the coarse separation of polyoxymethylene dimethyl ether is pumped into a lightness removal tower (1) for the first distillation separation: a removal gas A is produced at the top of the lightness removal tower (1), and a reaction liquid A (004) is obtained at the bottom of the lightness removal tower (1); S2: Vacuum tower unit process: The reaction liquid A (004) is pumped into a vacuum tower (7) through a discharge pump (6) of the tower kettle of the light-removing tower at one end of the tower bottom of the light-removing tower (1) to perform a second distillation separation: a discharge pump (9) of the tower kettle of the vacuum tower at one end of the tower bottom of the vacuum tower (7) is discharged to obtain a mixed liquid (005), and a mixed gas (006) is discharged from the top of the vacuum tower (7); wherein the mixed gas (006) is liquefied and enriched through a circulating cooling spray absorption system to obtain a low-aldehyde material; wherein the low-aldehyde material includes: a first part of low-aldehyde material (008), a second part of low-aldehyde material (009), and a third part of low-aldehyde material (010); S3: Pressurized tower unit process: The third part of low-aldehyde material (010) is pumped into the pressure tower (14) through the vacuum tower reflux pump (13) for the third distillation separation: the top of the pressure tower (14) produces a removal gas B, and the pressure tower kettle discharge pump (19) at one end of the bottom of the pressure tower (14) discharges the material to obtain trioxymethylene (013).

2. A process for refining trioxymethylene as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In S1, the first distillation separation condition is: under normal pressure, the temperature at the top of the light removal tower (1) is 50-80°C.

3. A process for refining trioxymethylene as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In S2, the second distillation separation conditions are: the temperature of the top of the vacuum tower (7) is 60-70°C; the pressure of the bottom of the vacuum tower (7) is 0.03-0.06MPa, and the temperature is 80-95°C.

4. A process for refining trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In S3, the third distillation separation conditions are: the pressure of the bottom of the pressure tower (14) is 0.25-0.45 MPa, and the temperature is 130-155°C; the pressure of the top of the pressure tower (14) is 0.20-0.40 MPa, and the temperature is 100-120°C.

5. A process for refining trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In the light removal tower unit process, a first condensation cooling reflux system is arranged at the top of the light removal tower (1) for treating and removing gas A; The treatment method is as follows: the removed gas A is sequentially treated by a light removal tower condenser (2), a light removal tower reflux tank (3), and a light removal tower reflux pump (4) to obtain a removed component A; wherein the removed component A comprises: a first removed component A (002) and a second removed component A (003); the first removed component A (002) continues to participate in the reflux reaction at the top of the light removal tower (1), and the second removed component A (003) is pumped to a methylal reaction unit to further synthesize methylal.

6. A process for refining trioxymethylene as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In the vacuum tower unit process, a circulating cooling spray absorption system is arranged at the top of the vacuum tower (7) for treating the mixed gas (006); The treatment method is as follows: the mixed gas (006) is liquefied and enriched in a vacuum spray tank (10) to obtain a low-aldehyde material; the first part of the low-aldehyde material (008) is sequentially treated by a vacuum tower reflux pump (13) and a vacuum cooler (12) for a reflux reaction in the vacuum tower spray tank (10); the second part of the low-aldehyde material (009) is pumped into a vacuum tower (7) through a vacuum tower reflux pump (13) to participate in a reflux reaction at the top of the vacuum tower (7); the third part of the low-aldehyde material (010) is pumped into a pressure tower (14) through a vacuum tower reflux pump (13) to continue a third distillation separation; the material (007) that is not absorbed is discharged through a vacuum pump (11).

7. A process for refining trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether according to claim 6, characterized in that: The connection mode of each device of the circulating cooling spray absorption system at the top of the vacuum tower (7) is as follows: the top of the vacuum tower (7) is connected to the space above the bottom liquid level of the vacuum tower spray tank (10) through a gas phase pipeline, and the gas phase is evenly distributed in the form of a row pipe; the inlet of the vacuum tower cooler (12) is connected to the outlet of the vacuum tower reflux pump (13); the outlet of the vacuum tower cooler (12) is connected to the space above the packing section at the top of the vacuum tower spray tank (10), and the liquid phase is evenly distributed in the form of a row pipe; the inlet of the vacuum pump (11) is connected to the gas phase space at the top of the vacuum tower spray tank (10).

8. A process for refining trioxymethylene as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: In the pressurized tower unit process, a second condensation cooling reflux system is provided at the top of the pressurized tower (14) for treating and removing gas B; The treatment method is as follows: the removal gas B is sequentially treated by a pressurized tower condenser (15), a pressurized tower reflux tank (16), and a pressurized tower reflux pump (17) to obtain a removal component B; wherein the removal component B includes: a first removal component B (011) and a second removal component B (012); the first removal component B (011) continues to participate in the top reflux reaction of the pressurized tower (14), and the second removal component B (012) is added to the polyoxymethylene dimethyl ether reaction system.

9. A process for refining trioxymethylene as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: A light-removal tower reboiler (5) is provided at the other end of the bottom of the light-removal tower (1); a vacuum tower reboiler (8) is provided at the other end of the bottom of the vacuum tower (7); and a pressure tower reboiler (18) is provided at the other end of the bottom of the pressure tower (14).

10. A process for refining trioxymethylene produced as a byproduct of polyoxymethylene dimethyl ether according to claim 1, characterized in that: The light removal tower (1), vacuum tower (7) and pressure tower (14) all use bubble cap or float valve trays to increase liquid holding capacity.

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