A polyoxymethylene dimethyl ethers heavy component decomposition device and process

Abstract

The application discloses a polyoxymethylene dimethyl ethers heavy component decomposition device and process, relates to the polyoxymethylene dimethyl ethers separation and recovery technical field, and the device includes pre-reactor, reaction tower, heavy oil pump, reaction kettle and circulating reactor which are sequentially communicated; the process steps include that the initial reaction of the mixed solution of polyoxymethylene dimethyl ethers synthesis heavy component and methylal is completed in the pre-reactor, and the polymer part in the pre-reactor is partially decomposed into the reaction liquid of oligomerization state; the reaction liquid is countercurrently contacted with methylal in the reaction tower and is further reacted on the catalytic bed; the polyether pump of the high polymer that is not completely decomposed in the reaction tower is pumped to the reaction kettle, and the methylal and water with relatively lower boiling point are generated in the circulating reactor with the supplement of methanol, and the synthesis water promotes the decomposition of the heavy component; the application realizes the recovery of high-value raw materials, completely decomposes the difficult-to-decompose heavy component, avoids many problems such as the difficulty in by-product sales and storage, and improves economic benefits.

Description

Technical Field

[0001] This invention relates to the field of polyoxymethylene dimethyl ether (POMED) separation and recovery technology, and particularly to a device and process for decomposing heavy components of POMED. Background Technology

[0002] Polyoxymethylene dimethyl ether (DMMn or PODEn) is an oxygen-containing compound with the general formula CH3O(CH2O)nCH3, where n is an integer ≥1 (generally less than 10, with n=2-5 being optimal for market demand; DMMn with different n values ​​will be referred to as DMMn below). Polymers of DMM3-5 not only have suitable flash points and boiling points, but also high oxygen content (47-49%) and cetane number (78-100), which are beneficial for improving the combustion of diesel fuel in engines, increasing thermal efficiency, and reducing pollutant emissions. Therefore, DMM3-5 is an ideal component for diesel engine fuel additives with great application prospects, and the preparation of DMMn has received widespread attention in recent years.

[0003] Current DMMn synthesis routes use methylal and formaldehyde as raw materials. Formaldehyde exists in various forms, including paraformaldehyde, polyformaldehyde, aqueous formaldehyde solutions, high-concentration aqueous formaldehyde solutions, and gaseous formaldehyde. In methods using formaldehyde and methylal as raw materials to synthesize DMMn, the formation of the polymeric DMM5+ component is inevitable. The heavier component has a higher boiling point and freezing point, and the more polymeric component is solid at room temperature but can be melted into a liquid upon heating. Currently, market demand is limited, and transportation and storage are difficult. During production, a portion is decomposed in a fixed-bed decomposition process, with the excess undecomposed component sent to the incineration unit to produce steam, further wasting raw materials and increasing production costs.

[0004] Patent CN103626640A describes a process and method for preparing polyoxymethylene dimethyl ether (POD). This method uses readily available and inexpensive methylal and formaldehyde as raw materials and employs a longer-lasting solid acid resin as a catalyst to synthesize POD. The patent addresses the treatment of heavy components by pumping the DMM5+ component obtained from the reactor bottom back to the reactor feed inlet. This component is then recycled with the formaldehyde aqueous solution to participate in the reaction and undergoes further distillation and purification. The entry of heavy components into the reactor not only increases the reaction system temperature, further reducing the formaldehyde conversion rate, but more importantly, the heavy components cannot be completely decomposed, ultimately leading to the enrichment of heavy components within the process system.

[0005] Patent CN112225649BCN103848730B describes a production apparatus and process for polyoxymethylene dimethyl ether (PODE). Unreacted methylal, formaldehyde, PODE2, and PODE5-8 are separated by distillation and then returned to the reactor for further reaction, thus increasing the yield of the target product PODE3-4. However, this patent also suffers from the problem of temperature rise caused by the return of the heavy component DMM5-8 to the upstream reaction system, which inhibits the reaction and leads to the recycling and enrichment of heavy components.

[0006] Most current patents addressing heavy components involve returning them to the upstream reaction system, including fixed-bed reactors and catalytic converters. This not only affects the temperature of the upstream reaction system, reducing reaction conversion rates, but also increases the system's circulation volume due to the large amount of heavy components recycled, ultimately leading to an increase in the size of various system components. Furthermore, the incineration of some unprocessable heavy components further increases production costs. Summary of the Invention

[0007] To avoid waste of raw materials and prevent the deterioration of the operating environment caused by the recycling of heavy components to the synthesis unit under normal operating conditions, thereby improving the conversion rate of polyether synthesis, this invention provides a polyoxymethylene dimethyl ether heavy component decomposition device and process.

[0008] The technical solution of this invention is as follows: A polyoxymethylene dimethyl ether (POD) heavy component decomposition device includes a pre-reactor, a reaction tower, a reaction vessel, and a circulating reactor connected sequentially by pipelines. The reaction tower includes a catalytic reaction section and a stripping section from top to bottom. The pre-reactor has a pre-reactor inlet at the top and a pre-reactor outlet at the bottom. The pre-reactor outlet is connected to the upper inlet of the catalytic reaction section of the reaction tower. The reaction tower also has a middle inlet, a bottom outlet, and a top outlet. The bottom outlet of the reaction tower is connected to the reaction vessel inlet via a heavy oil pump. The reaction vessel has a vaporization port at the top. The circulating reactor has a circulating reactor inlet at the top and a circulating reactor outlet at the bottom. The circulating reactor inlet and outlet are connected to the circulating reactor via a circulating pump. A methanol replenishment port is provided on the circulating reactor inlet pipeline.

[0009] Furthermore, a reaction tower regulating valve is installed at the top outlet of the reaction tower, and a reboiler is installed at the bottom of the reaction tower; a reaction vessel regulating valve is installed at the top vaporization port of the reaction vessel, and a jacket is installed at the bottom of the reaction vessel.

[0010] A method for decomposing heavy components of polyoxymethylene dimethyl ether includes the following steps: S1. The heavy component and methyl acetal undergo a preliminary decomposition reaction in the pre-reactor to generate formaldehyde and low-polymerization degree polyoxymethylene dimethyl ether. S2. The undecomposed heavy components and the generated formaldehyde in step S1 come into countercurrent contact with methyl acetal and react in the catalytic reaction section of the reaction tower. The light components are collected from the top outlet of the reaction tower, and the residual high-boiling heavy components that have not been completely reacted fall into the bottom of the reaction tower. S3. The remaining high-boiling-point heavy components that have not been completely reacted are pumped into the reactor by a heavy oil pump and undergo further reforming reaction with the supplemented methanol in the circulating reactor. The resulting light components are taken out from the vaporization port at the top of the reactor.

[0011] Furthermore, in step S1, the mass ratio of the heavy component to methyl acetal is 1-10:1, and the reaction temperature of the preliminary decomposition reaction is 90-130℃.

[0012] The pre-reactor is used to pump preheated methyl acetal and polyether heavy components (mainly DMM5+) to a certain temperature into the pre-reactor, where the heavy components undergo preliminary decomposition.

[0013] The amount of methylal added is proportional to the formaldehyde content in the heavy component. This invention uses the mass ratio of the heavy component (with formaldehyde content taken into account) to the mass of methylal as a reference. The addition of methylal further controls the reaction temperature of the pre-reactor to not exceed the optimal operating range of the resin catalyst.

[0014] Inside the reaction tower, the undecomposed heavy components and the generated formaldehyde come into countercurrent contact with the methyl acetal supplemented in the lower section of the tower as they pass through the catalyst bed from top to bottom, and further react on the catalyst packing inside the tower. The components with relatively low boiling points and unconverted methyl acetal are collected from the top of the column and sent to the polyether synthesis unit for further recovery of effective raw materials.

[0015] Furthermore, in step S2, the light component reaction gas includes methyl acetal, methanol, water, and DMMn (n=2-4); the pressure of the regulating tower reaction tower is 0-0.5 MPa, and the temperature of the reaction section of the tower reaction tower is 80-120℃; the mass ratio of the undecomposed heavy component and the generated formaldehyde to methyl acetal is 1-8:1.

[0016] The pressure control valve at the top of the reaction tower regulates the pressure inside the tower and the gas output.

[0017] The amount of methyl acetal added to the bottom of the reaction section of the reaction tower is closely related to the degree of polymerization of polyether and the reaction conversion rate of the pre-reactor. Controlling the amount of methyl acetal added to the reaction section is beneficial to maintaining a suitable reaction temperature in the tower.

[0018] The reactor is fed with unreacted polyether reaction liquid containing high polymers, enriched in the bottom of the reaction tower. This component is pumped into the reactor via a heavy oil pump. Optionally, the reactor is filled with a catalyst module wrapped in wire mesh; in this embodiment of the reactor system, only the external circulation reactor is filled with catalyst.

[0019] The material discharged from the bottom of the reactor is pumped to the circulating reactor by a circulating pump and then returned to the reactor. Gas-liquid separation occurs in the gas phase space of the reactor, and the gas phase is distilled out from the top pipe to the methyl acetal synthesis unit. The circulating reactor is filled with a solid acid catalyst.

[0020] The main reactions occurring on the catalyst inside the reactor and the catalyst in the circulating reactor are the synthesis of methyl acetal from methanol and formaldehyde, the decomposition of high-polymerization-degree polyether into low-polymerization-degree polyether and formaldehyde.

[0021] Light components such as methyl acetal, water, methanol, DMM2, and a small amount of free formaldehyde are vaporized from the top of the tower, further promoting the decomposition of polyether. After multiple cycles, the polyether polymer is finally completely decomposed into low-boiling-point components, which are then collected from the top of the reactor.

[0022] Furthermore, in step S3, the pressure in the reactor is 0.1-0.8 MPa; the temperature inside the reactor is 90-130℃.

[0023] Furthermore, in step S3, methanol is added to the feed of the circulating reactor. The formaldehyde produced by the decomposition of the heavy components reacts with methanol to generate methyl acetal and water. The methyl acetal and water vaporize out of the reactor to promote the forward reaction.

[0024] Furthermore, in step S3, the ratio of methanol replenishment to reactor feed mass is 0.1-5:1, and the operating temperature of the circulating reactor is 90-140℃.

[0025] The pressure inside the tower and the gas outflow rate are regulated by the pressure control valve at the top of the tower, allowing the gas to be further decomposed and synthesized into methyl acetal in the methyl acetal synthesis unit. Low-pressure saturated steam is preferred as the jacket heating medium to maintain a stable reactor temperature.

[0026] A certain proportion of methanol is added to the circulating reactor to further react with the residual heavy components to produce methylal and water; the amount and temperature of methanol addition can further regulate the temperature inside the reactor, which can extend the life of the resin catalyst.

[0027] Furthermore, the pre-reactor, reaction tower, and circulating reactor are all filled with catalyst.

[0028] Furthermore, the catalyst in the pre-reactor is an acidic cation exchange resin with a temperature resistance of not less than 140°C, and the loading amount is 100-900 kg / m³. 3 The catalyst inside the reaction tower is an acidic cation exchange resin with a temperature resistance of not less than 120℃, and the loading rate is 100-500 kg / m³. 3 The catalyst in the circulating reactor is an acidic cation exchange resin with a temperature resistance of not less than 150℃, and the loading rate is 100-900 kg / m³. 3 .

[0029] Explanation of chemical molecular formula: Methanol CH3OH; Formic acid HCOOH; Trioxymethylene [CH2O]3; Formaldehyde CH2O; Methyl acetal (DMM1) CH3O-[CH2O]1-CH3; Dimethyl dimethyl acetal (DMM2): CH3O-[CH2O]2-CH3; Dimethyl trimethyl acetal (DMM3): CH3O-[CH2O]3-CH3; Dimethyl tetramethyl acetal (DMM4); Dimethyl pentamethyl acetal (DMM5); Dimethyl hexamethyl acetal (DMM6); Dimethyl heptamethyl acetal (DMM7).

[0030] Boiling point explanation: Methyl acetal (DMM1): 42℃; Methanol: 64℃; Formic acid: 101℃; Formaldehyde monomer: -19℃; Dimethyl acetal (DMM2): 105℃; Dimethyl acetal (DMM3): 155℃; Dimethyl acetal (DMM4): 205℃; Dimethyl acetal (DMM5): 255℃; Trioxymethylene [CH2O]3: 114℃; Paraformaldehyde [CH2O] n Boiling point increases with increasing degree of polymerization, mostly within the range of 100-150℃.

[0031] Azeotropic description: Azeotropic point of methyl acetal and methanol: 42℃, mass ratio (90-94)% : (6-10)%; Azeotropic point of water and trioxymethylene: 91℃, mass ratio 30% : 70%; Azeotropic point of water and formic acid: 107℃, mass ratio 26% : 74%; Azeotropic point of water and DMM2: 50-80℃; Note: Formaldehyde in water mostly exists in the form of methyl glycol, and a small amount combines with methanol to synthesize hemiacetal. Both have thermal decomposition characteristics, and the decomposition accelerates with increasing temperature.

[0032] The reaction equation involved in this invention is as follows:

[0033] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a process for the decomposition of heavy components of polyoxymethylene dimethyl ether (POMED). The heavy components undergo a preliminary reaction with methylal in a pre-reactor. The resulting reaction solution is further reacted in a catalytic reaction tower to obtain more gaseous materials with the DMM2-4 product structure of the POMED, ​​which are then collected from the top of the tower, achieving the recovery of high-quality intermediate products and raw materials. Unconverted POMED in the reactor bottom reacts with methanol in both the reactor and the circulating reactor. The simultaneous reaction and separation design greatly promotes the forward movement of the target reaction, completely decomposing the heavy components into methylal for recovery. This process has high raw material recovery efficiency, reduces ineffective system circulation, and consequently reduces steam consumption, making it a valuable production process.

[0034] This invention involves pre-reacting heavy components with methylal on a catalyst in a pre-reactor, followed by further reaction in a catalytic tower to convert them into DMMn (mainly n=2-4) with lower polymerization degrees and formaldehyde. The gas phase is then sent to the DMMn synthesis unit for reuse. Unconverted polymers in the reactor and circulating reactor react further with supplemented methanol. The rapid vaporization of lower-boiling-point products methylal and water promotes a more complete reaction conversion, and the gas phase is sent to the methylal synthesis unit to recover the raw materials. This invention avoids raw material waste, prevents the deterioration of the operating environment caused by recycling heavy components to the synthesis unit under conventional conditions, and thus improves the polyether synthesis conversion rate. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the device of the present invention; Explanation of reference numerals in the attached figures: K01. Pre-reactor, K02. Reaction tower, K03. Reboiler, K04. Heavy oil pump, K05. Reactor, K06. Circulating pump, K07. Circulating reactor.

[0036] ①. Catalytic reaction section, ②. Stripping section, ③. Reactor regulating valve, ④. Reactor regulating valve, ⑤. Jacket. Detailed Implementation

[0037] Device Examples like Figure 1As shown, a polyoxymethylene dimethyl ether (POD) heavy component decomposition device includes a pre-reactor K01, a reaction tower K02, a reaction vessel K05, and a circulating reactor K07 connected in sequence. The pre-reactor K01 has a feed inlet at the top and a discharge outlet at the bottom. The discharge outlet is connected to the upper feed inlet of the reaction tower K02. The reaction tower K02 also has a middle feed inlet, a bottom discharge outlet, and a top outlet. The reaction tower K02 includes, from top to bottom, a catalyst... The reactor consists of a reaction section ① and a stripping section ②. A reaction tower regulating valve ③ is installed at the top outlet of the reaction tower. A reboiler K03 is installed at the bottom of the reaction tower K02. The bottom outlet of the reaction tower is connected to the inlet of the reactor K05 via a heavy oil pump K04. A vaporization port is installed at the top of the reactor K05. The inlet and outlet of the circulating reactor K07 are connected to the circulating reactor K07 via a circulating pump K06. A methanol replenishment port is installed on the inlet pipeline of the circulating reactor K07. A reactor regulating valve ④ is installed at the top outlet of the reactor K05, and a jacket ⑤ is installed at the bottom of the reactor K05.

[0038] Process Example 1: The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Please see Figure 1 A preferred embodiment of the present invention provides a process for the decomposition of heavy components of polyoxymethylene dimethyl ether, which mainly includes a pre-reactor K01, a reaction tower K02, a reaction vessel K05, a circulating reactor K07, a reboiler, and a pressure control system.

[0040] Feed material 1 (stream r01) is the heavy component produced after the polyether unit is refined (flow rate: 1000 kg / h, DMM4: 10%, DMM5: 60%, DMM6: 30%, a small amount of light component impurities). This material is mixed with the supplemented methylal (stream r02, flow rate: 215.1 kg / h, DMM1: 93%, methanol: 7.0%, a small amount of light component impurities) and then pumped into the pre-reactor K01.

[0041] Higher temperatures increase the reaction conversion rate and simultaneously promote the reaction equilibrium of the hydrolysis of the heavy component in the endothermic reaction. Adjusting the temperature of the feed components greatly promotes the target reaction. In Example 1, the feed temperature was controlled at 105-115℃, and the reactor pressure was controlled at 0.3-0.8 MPa to avoid vaporization of methyl acetal.

[0042] The polyether heavy component (mainly DMM5+) is initially decomposed and reformed in the pre-reactor K01. The amount of methylal added is proportional to the formaldehyde content in the heavy component; for easy calculation, the preferred mass ratio of heavy component (stream r01) to methylal (stream r02) is 1-10:1, and the ratio in Example 1 is adjusted to 4.65:1.

[0043] The formaldehyde content in the reaction solution can be further controlled by supplementing the amount of methyl acetal to avoid excessive formaldehyde concentration and polymerization. At the same time, reasonable formulation can control the conversion of the target product to the DMM2-4 range.

[0044] Because the boiling points of the light and heavy components differ significantly, the feed from the top of reaction tower K02 is simultaneously refluxed. The proportion of methyl acetal in the feed can be adjusted appropriately based on the separation efficiency.

[0045] Inside reaction tower K02, heavy components and formaldehyde come into countercurrent contact with methyl acetal replenished in the lower section of the tower as they pass through the catalytic bed from top to bottom and react. A high concentration (preferably 90-94%) of methyl acetal (stream r04, flow rate: 215.1Kg / h, DMM1: 93%, methanol: 7%, small amount of water impurities) is replenished to the bottom space of the catalytic reaction section ① of the reaction tower.

[0046] The reaction produces relatively low-boiling-point reaction gases (DMM2-4) and unreacted methylal, methanol, etc., which are collected from the top of the tower and sent to the polyether synthesis unit (stream r05, flow rate: 1209.8 kg / h, formaldehyde: 18.93%, methanol: 0.19%, water: 0.64%, trioxymethylene: 3.30%, DMM1: 29.11%, DMM2: 31.67%, DMM3: 10.65%, DMM4: 4.35%, DMM5: 1.11%, DMM6: 0.04%, and a small amount of light component impurities). This stream of material has relatively low amounts of methanol and water impurities, and is of high quality, meeting the material requirements of the polyether synthesis unit.

[0047] Adjusting the opening of the regulating valve ③ at the top of reaction tower K07 further controls the pressure and temperature of reaction tower K07. Higher temperatures can accelerate the decomposition of the target reactants, but excessively high temperatures can lead to the formaldehyde disproportionation reaction in the system generating too much formic acid, further corroding the equipment and increasing the difficulty of subsequent product separation and purification.

[0048] The pressure control valve regulates the pressure inside the tower and the gas output. The preferred tower pressure is 0-0.5 MPa, and the preferred temperature in the catalytic reaction zone is 80-120℃.

[0049] The amount of methylal added to the bottom of the reaction section of the reaction tower is closely related to the degree of polymerization of the polyether and the reaction status of the pre-reactor K01. Maintaining a suitable reaction temperature in the tower further controls the feed rate of the methylal. The preferred mass flow ratio of the pre-reactor outlet (stream r03) to the amount of methylal added to the bottom of the catalytic reaction section ① (stream r04) is 1-8:1, with a ratio of 5.65:1 in Example 1. This ratio is adjusted appropriately based on sampling and analysis, and considering the temperature and pressure parameters within the tower.

[0050] The reaction section is a reaction structure in which the catalyst is wrapped in packing material. To ensure sufficient reaction time and a reasonable gas-liquid load, the preferred catalyst loading in the catalytic reaction section is approximately 100-500 kg / m³. 3 In Example 1, the catalyst loading was approximately 300 kg / m³. 3 .

[0051] Furthermore, to achieve free control over the content of the target product in the reactants and control the reactant concentration, 3-6 external reactors can be set up. The amount of methylal added to the external reactors can be reasonably adjusted according to the content of the material extracted from the tower and the reaction status, so as to achieve more efficient control of the reaction process.

[0052] For the stripping section ② of the reaction tower, a tray tower with larger openings is preferred, with floating valves and bubble caps being the best options.

[0053] After further purification in the bottom stripping section ② of the reaction tower, the heavy components with lower light component content are enriched in the bottom of the tower and collected by heavy oil pump K04 into reactor K05 (stream r06, flow rate: 220.3 kg / h, formaldehyde: 4.33%, methanol: 0.06%, water: 0.04%, trioxymethylene: 0.37%, DMM1: 0.02%, DMM2: 2.11%, DMM3: 5.09%, DMM4: 10.24%, DMM5: 54.75%, DMM6: 23.01%, small amount of light component impurities). Reactor K05 is filled (optional) with a certain amount of reaction packing material containing a catalyst wrapped in wire mesh.

[0054] The enriched material in reactor K05 is pumped to circulating reactor K07 via circulating pump K06. Circulating reactor K07 is filled with an acidic catalyst, where the reaction of methanol and formaldehyde to synthesize methyl acetal and water takes place. Supplemental methanol (stream r10, flow rate: 200 kg / h) is pumped into circulating reactor K07 through the inlet, and its supplemental amount is positively correlated with the polymer content and degree of polymerization of the feed polymer to the reactor. The preferred ratio of methanol to feed mass flow rate is (0.1-5):1; in Example 1, the ratio is approximately 0.91:1.

[0055] Light components such as methylal, water, methanol, DMM2, and a small amount of free formaldehyde are vaporized from the top of the column (stream r08, flow rate: 420.3 kg / h, formaldehyde: 8.55%, methanol: 5.05%, water: 11.99%, trioxymethylene: 0.19%, DMM1: 67.61%, DMM2: 5.48%, DMM3: 0.96%, DMM4: 0.16%, DMM5: 0.0%, DMM6: 0.0%, and a small amount of light component impurities), which further promotes the decomposition of polyether into low-polymerization-degree materials and formaldehyde. After multiple cycles, the polyether is finally decomposed into low-boiling-point components and collected from the top of the reactor.

[0056] After the reaction, the material is pumped back to the gas phase space of the reactor. Through multiple cycles of circulation, reaction, and flash evaporation, the heavy components are completely converted into low-boiling-point methylal, water, DMM2-4, and other materials. This group of materials is then vaporized via reactor regulating valve ④ to the methylal synthesis unit, further achieving complete decomposition of the heavy components and recycling of raw materials.

[0057] The circulating reactor K07 is filled with a solid acid catalyst, preferably a temperature-resistant acidic resin catalyst, at a loading rate of 100-900 kg / m³. 3 Example 1 contains 500 kg / m³ 3 Catalyst.

[0058] The pressure inside the tower and the gas outflow rate are regulated by the pressure control valve at the top of the tower, and the gas is further decomposed and synthesized into methyl acetal in the methyl acetal synthesis unit. In Example 1, the pressure in the reactor is controlled at 0.3-0.5 MPa and the temperature at 100-110℃.

[0059] Process Example 2: In the experiment, the concentration and ratio of the feed raw materials were adjusted and the experimental data were compared and analyzed to verify Example 2.

[0060] The feed material, consisting of heavy components (stream r01, flow rate: 1000 kg / h, DMM4: 20%, DMM5: 20%, DMM6: 60%, and a small amount of light component impurities), is mixed with supplemental methylal (stream r02, flow rate: 279.6 kg / h, DMM1: 93%, methanol: 7.0%, and a small amount of light component impurities) and then pumped into the reaction tower (K01).

[0061] Adjust the temperature of the feed methyl acetal and the heavy component. In Example 2, control the feed temperature at 110-119℃ and the reactor feed pressure at 0.3-0.8 MPa.

[0062] The polyether heavy component (mainly DMM5+) is initially decomposed and reformed in the pre-reactor K01. The amount of methylal added is proportional to the formaldehyde content in the heavy component. To facilitate the calculation of the ratio of heavy component (stream r01) to methylal (stream r02), a ratio of 1-10:1 is preferred. In Example 2, the ratio is 3.58:1.

[0063] Inside reaction tower K02, a high concentration (preferably 90-94%) of methylal (stream r04, flow rate: 236.6 kg / h, DMM1: 93%, methanol: 7%, with a small amount of water and impurities) is pumped into the bottom space of the catalytic reaction section ① of the reaction tower.

[0064] The reaction produces relatively low-boiling-point reaction gases (DMM2-4) and unreacted methyl acetal, methanol, etc., which are collected from the top of the tower and sent to the polyether synthesis unit (stream r05, flow rate: 1208.6 kg / h, formaldehyde: 14.95%, methanol: 0.70%, water: 0.63%, trioxymethylene: 3.61%, DMM1: 30.49%, DMM2: 34.6%, DMM3: 9.66%, DMM4: 4.76%, DMM5: 0.51%, DMM6: 0.09%, and a small amount of light component impurities).

[0065] Adjusting the opening degree of the regulating valve ③ at the top of the reaction tower further controls the pressure and temperature of the reaction tower. In Example 2, the reaction tower pressure is 0.3-0.5 MPa, and the preferred temperature in the catalytic reaction zone is 100-120℃.

[0066] The amount of methyl acetal added to the bottom of the reaction section of the reaction tower is closely related to the degree of polymerization of polyether and the reaction status of the pre-reactor. The preferred mass flow ratio of the pre-reactor outlet (stream r03) to the amount of methyl acetal added to the bottom of the catalytic reaction section ① (stream r04) is 1-8:1. In Example 2, the ratio is 5.41:1.

[0067] The reaction section is a reaction structure in which the catalyst is wrapped in packing material. To ensure sufficient reaction time and a reasonable gas-liquid load, the preferred catalyst loading in the catalytic reaction section is approximately 100-500 kg / m³. 3 In Example 2, the catalyst loading was approximately 300 kg / m³. 3 .

[0068] After further purification in the bottom stripping section ② of the reaction tower, the bottom material is pumped out by heavy oil pump K04 into the reaction vessel K05 (material r06, flow rate: 307.6 kg / h, formaldehyde: 2.45%, methanol: 0.15%, water: 0.02%, trioxymethylene: 0.29%, DMM1: 0.01%, DMM2: 1.65%, DMM3: 13.34%, DMM4: 8.01%, DMM5: 38.11%, DMM6: 35.98%, with a small amount of light component impurities).

[0069] The enriched material in the reactor is pumped to the circulating reactor K07 via circulating pump K06. Methanol (r10, flow rate: 330 kg / h) is added through the inlet of the circulating reactor. The preferred ratio of methanol to feed mass flow rate is 0.1-5:1; in Example 2, the ratio is 1.07:1.

[0070] Light components, including methylal, water, methanol, DMM2, and a small amount of free formaldehyde, are vaporized at the top of the column (stream r08, flow rate: 637.6 kg / h, formaldehyde: 8.41%, methanol: 19.93%, water: 8.98%, trioxymethylene: 0.14%, DMM1: 52.91%, DMM2: 6.62%, DMM3: 2.32%, DMM4: 0.70%, DMM5: 0.0%, DMM6: 0.01%, and a small amount of light component impurities). This further achieves the complete decomposition of heavy components and the recovery and utilization of raw materials.

[0071] The circulating reactor K07 is filled with a solid acid catalyst, preferably an acidic resin catalyst resistant to 150℃, with a loading rate of 100-900 kg / m³. 3 Example 2: Filled with 500 kg / m³ 3 Catalyst.

[0072] The pressure inside the tower and the gas output flow rate are adjusted by the pressure control valve at the top of the tower. In Example 2, the pressure in the reactor is 0.5-0.8 MPa, and the temperature of the reactor jacket ⑤ is maintained at 110-130℃.

[0073] Comparing the two examples, the proportion of DMM6 in the heavy component feed (material r01) increased from 30% in Example 1 to 60% in Example 2, the degree of polymerization of the heavy component feed increased, and the formaldehyde produced by decomposition increased to a certain extent.

[0074] The ratio of methylal was further adjusted, decreasing from 4.65:1 in Example 1 to 3.58:1 in Example 2. The mass flow ratio of the supplemented methylal (r04 stream) was slightly reduced from 5.65:1 in Example 1 to 5.41:1. Changes in the amount of methylal supplemented and the content of the feed polyether significantly affected the recovery of the effective material (DMM2-4). In the top fraction obtained from the reaction tower, the mass flow rate of the effective component DMM2-4 increased from 564.6 kg / h in Example 1 to 592.4 kg / h in Example 2, and its proportion of total output increased from 46.67% to 49.01%. This further illustrates that higher polymerization degree feedstocks and a reasonable amount of methylal addition have a certain impact on the recovery of the effective component.

[0075] The yield from the reactor bottom increased from 220.3 kg / h to 269.5 kg / h, demonstrating that the amount of methylal supplemented to a certain extent has an impact on the decomposition and conversion of heavy components. More methylal can decompose to produce DMM2, a component with a lower degree of polymerization, while simultaneously promoting the decomposition efficiency of heavy components. However, the recovery rate of the effective component DMM2-4 at the top of the reactor decreased significantly. In summary, the proportion of methylal and the recovery of raw materials and the decomposition efficiency of heavy oil in the reactor have considerable adjustable range and can be adjusted as needed.

[0076] In the aforementioned reactor system, Example 1 supplements with methanol (r10, flow rate: 200 kg / h) at a ratio of approximately 0.91:1. Example 2 supplements with methanol (r10, flow rate: 330 kg / h) at a ratio of approximately 1.07:1. The preferred methanol-to-feed mass flow rate ratio is 0.1-5:1. The amount of methanol supplemented is positively correlated with the content of heavy components (especially formaldehyde) in the reactor bottom.

[0077] In summary, the degree of polymerization of the heavy components in the feed and the proportion of methylal in the feed directly affect the reaction equilibrium, and are closely related to the recovery of effective polyether components and the decomposition efficiency of the reactor. The amount of methylal added can be adjusted appropriately according to the conversion situation in the reactor and tower, and the ratio of the total mass of methylal added to the feed of heavy components can be increased to 1-15:1. The recovery rate of effective components increased from 57.8% in Example 1 to 60.0%. Therefore, reasonable formulation and operation have a positive effect on reducing feedstock recycling, reducing the amount of ineffective feedstock recycling, and further reducing steam consumption.

[0078] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A device for decomposing heavy components of polyoxymethylene dimethyl ether, characterized in that: The reactor comprises a pre-reactor (K01), a reaction tower (K02), a reaction vessel (K05), and a circulating reactor (K07), which are connected sequentially by pipelines. The reaction tower (K02) includes a catalytic reaction section (①) and a stripping section (②) from top to bottom. The pre-reactor (K01) has a feed inlet at the top and a discharge outlet at the bottom. The discharge outlet is connected to the upper feed inlet of the catalytic reaction section (①) of the reaction tower (K02). The reaction tower (K02) also has a bottom discharge outlet and a bottom outlet. The top outlet of the reaction tower is connected to the reactor inlet of the reactor (K05) via a heavy oil pump (K04). The reactor (K05) is equipped with a vaporization port at the top. The circulating reactor (K07) is equipped with a circulating reactor inlet at the top and a circulating reactor outlet at the bottom. The circulating reactor inlet and outlet of the circulating reactor (K07) are connected to the circulating reactor (K07) via a circulating pump (K06). A methanol replenishment port is provided on the feed pipeline of the circulating reactor (K07).

2. The polyoxymethylene dimethyl ether heavy component decomposition device according to claim 1, characterized in that: A reaction tower regulating valve (③) is installed at the top outlet of the reaction tower (K02), and a reboiler (K03) is installed at the bottom of the reaction tower (K02); a reaction vessel regulating valve (④) is installed at the top vaporization port of the reaction vessel (K05), and a jacket (⑤) is installed at the bottom of the reaction vessel (K05).

3. A process for decomposing heavy components of polyoxymethylene dimethyl ether, using the polyoxymethylene dimethyl ether heavy component decomposition device according to any one of claims 1-2, characterized in that: Includes the following steps: S1. The heavy component and methyl acetal undergo a preliminary decomposition reaction in the pre-reactor (K01) to generate formaldehyde and polyoxymethylene dimethyl ether. S2. The undecomposed heavy components and the generated formaldehyde in step S1 come into countercurrent contact with methyl acetal and react in the catalytic reaction section (①) in the reaction tower (K02). The light components are collected from the top outlet of the reaction tower, and the residual high-boiling heavy components that have not been completely reacted fall into the bottom of the reaction tower (K02). S3. The remaining high-boiling-point heavy components that have not been completely reacted are pumped to the reactor (K05) via the heavy oil pump (K04) and undergo further reforming reaction with the supplemented methanol in the circulating reactor (K07). The resulting light components are taken out from the vaporization port at the top of the reactor (K05).

4. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 3, characterized in that: In step S1, the mass ratio of the heavy component to methyl acetal is 1-10:1, and the reaction temperature of the initial decomposition reaction is 90-130℃.

5. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 3, characterized in that: In step S2, the light component reaction gas includes methyl acetal, methanol, water and DMMn (n=2-4); the pressure of the reaction tower (K02) is 0-0.5 MPa, and the temperature of the reaction section of the reaction tower (K02) is 80-120℃; the mass ratio of the undecomposed heavy component and the generated formaldehyde to methyl acetal is 1-8:

1.

6. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 3, characterized in that: In step S3, the pressure in the reactor (K05) is 0.1-0.8 MPa; the temperature inside the reactor (K05) is 90-130℃.

7. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 3, characterized in that: In step S3, methanol is added to the feed of the circulating reactor (K07). The formaldehyde produced by the decomposition of heavy components reacts with methanol to generate methyl acetal and water. The methyl acetal and water vaporize out of the reactor (K05) to promote the forward reaction.

8. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 7, characterized in that: In step S3, the ratio of methanol replenishment to reactor feed mass is 0.1-5:1, and the operating temperature of the circulating reactor (K07) is 90-140℃.

9. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 3, characterized in that: The pre-reactor (K01), reaction tower (K02), and circulating reactor (K07) are all filled with catalyst.

10. The polyoxymethylene dimethyl ether heavy component decomposition process according to claim 9, characterized in that: The catalyst in the pre-reactor (K01) is an acidic cation exchange resin with a temperature resistance of not less than 140℃, and the loading amount is 100-900 kg / m³. 3 The catalyst in the reaction tower (K02) is an acidic cation exchange resin with a temperature resistance of not less than 120℃, and the loading amount is 100-500 kg / m³. 3 The catalyst in the circulating reactor (K07) is an acidic cation exchange resin with a temperature resistance of not less than 150℃, and the loading amount is 100-900 kg / m³. 3 .

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