Device and method for producing concentrated formaldehyde by oxidizing methylal

Abstract

The present invention provides an apparatus and method for producing concentrated formaldehyde by oxidizing methylal, relating to the technical field of chemical production. The apparatus comprises: a methylal unit 15, a methylal vaporizer 1, a fresh air blower 9, a thermal oil heat exchanger 11, and a concentrated formaldehyde heater 12, followed in sequence by a circulating air pressurizing blower 7, a circulating air mixer 8, a reactor inlet and outlet air heat exchanger 2, a methylal oxidation reactor 3, a reactor inlet and outlet air heat exchanger 2, a formaldehyde absorption tower 4, a circulating air dehumidifier 5, a gas-liquid separator 6, and an absorption tail gas treatment device 14. The circulating air mixer 8 is connected upstream to the methylal vaporizer 1; the gas-liquid separator 6 is connected upstream to the fresh air blower 9; the methylal oxidation reactor 3 is connected to the thermal oil heat exchanger 11; and the formaldehyde absorption tower 4 is connected to the concentrated formaldehyde heater 12. The present invention solves the problem of dilute formaldehyde treatment in formaldehyde-related processes by using dilute formaldehyde produced as a byproduct of the process and methanol as a raw material.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, and in particular to a device and method for preparing concentrated formaldehyde by oxidizing methylal. Background Art

[0002] The production of materials such as paraformaldehyde, polyoxymethylene dimethyl ether, methyl acrylate, and polyoxymethylene all uses concentrated formaldehyde as the main raw material. Currently, there are two main methods for preparing formaldehyde: direct oxidation of methanol and methylal oxidation.

[0003] Direct methanol oxidation processes can be categorized as silver and iron-molybdenum based on the catalyst used. For example, Chinese patent CN107501060A discloses a concentrated formaldehyde production process. Formaldehyde is produced through direct methanol oxidation, with the bottom discharge of the formaldehyde concentrator producing a concentrated formaldehyde solution with a formaldehyde mass fraction exceeding 60%. However, this method requires enormous amounts of energy for wastewater treatment, resulting in high energy consumption and environmental risks.

[0004] The methylal process involves synthesizing methylal from dilute formaldehyde and methanol under the catalysis of a solid acid, obtaining high-concentration methylal at a low energy cost. Methylal is then further oxidized and absorbed to yield concentrated formaldehyde.

[0005] Chinese patent CN20852196U discloses a device for producing concentrated formaldehyde. The device's workflow involves mixing pressurized air with vaporized methylal to react in a catalytic unit. The reacted material undergoes heat recovery and cooling, and finally, an absorption unit extracts approximately 55% of the concentrated formaldehyde. The resulting concentrated formaldehyde concentration is generally below 60%, which cannot meet market demand for high-concentration formaldehyde.

[0006] Traditional concentrated formaldehyde production processes typically use falling / rising film vacuum evaporation to concentrate 45-55 wt% formaldehyde to a 65-70 wt% concentrate. This concentrated formaldehyde is then converted into the corresponding products through a series of process steps. Both during the evaporation and concentration process and in subsequent production processes, large amounts of dilute formaldehyde are generated. Dealing with this dilute formaldehyde has become a challenge for manufacturers of paraformaldehyde, polyoxymethylene dimethyl ether, methyl acrylate, and polyoxymethylene.

[0007] At present, most of the dilute aldehyde pressure distillation methods are used to recycle dilute aldehyde. However, the pressure distillation process has serious formaldehyde disproportionation, serious equipment corrosion, high equipment material requirements, relatively large investment, high energy consumption, and waste of resources. In addition, only <45wt% formaldehyde can be obtained, and subsequent vacuum falling film / rising film evaporation is required to further concentrate to obtain 65-70wt% concentrated formaldehyde. Since the existing technology often has high requirements for the concentration of formaldehyde products when using formaldehyde products, the value of dilute formaldehyde solutions as products is relatively low. Therefore, how to handle dilute formaldehyde, give full play to its maximum value with minimum energy consumption, and drive the market is a research focus in this field. It is also a problem that needs to be solved urgently by those in this field.

[0008] Based on this, it is of great significance to develop a production device and method for producing concentrated formaldehyde by oxidizing methylal: on the one hand, the effective utilization of the by-product dilute formaldehyde in the process of preparing polyformaldehyde, polyoxydimethyl ether, methyl acrylate and polyformaldehyde from concentrated formaldehyde can solve the problem of dilute formaldehyde treatment; on the other hand, it can reduce the energy consumption and operating costs of the process. Summary of the Invention

[0009] To address the above-mentioned issues, the present invention provides an apparatus and method for producing concentrated formaldehyde by oxidizing methylal. Through a rationally designed apparatus structure, the dilute methylal produced as a byproduct during the process is used as a raw material, reacted with methanol, and refined. Through precise temperature control during the reaction, 95% to 98.5% methylal is obtained. Methylal is oxidized and absorbed to produce concentrated formaldehyde, and the dilute methylal produced in subsequent processes is recovered and further used as a raw material for synthesizing methylal.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] In one aspect, the present invention provides an apparatus for producing concentrated formaldehyde by oxidizing methylal, comprising: a methylal unit, a methylal gasifier, a fresh air blower, a thermal oil heat exchanger, a concentrated formaldehyde heater, a circulating gas pressurizing blower, a circulating gas mixer, a reactor inlet and outlet air heat exchanger, a methylal oxidation reactor, a formaldehyde absorption tower, a circulating gas dehumidifier, a gas-liquid separator, and an absorption tail gas treatment device connected in sequence;

[0012] The upstream of the circulating gas mixer is connected to a methylal gasifier;

[0013] The gas-liquid separator is connected upstream to a fresh air blower;

[0014] The methylal oxidation reactor is connected to a thermal oil heat exchanger;

[0015] The formaldehyde absorption tower is connected to a concentrated formaldehyde heater.

[0016] Preferably, the methylal gasifier is connected to low-grade steam.

[0017] Preferably, the first stage of the reactor inlet and outlet air heat exchanger is connected to a boiler water high level tank.

[0018] Preferably, the circulating cooler is connected to the tower side of the formaldehyde absorption tower.

[0019] Preferably, the concentrated aldehyde heater is connected to low-grade steam.

[0020] Preferably, the tail gas from the top of the formaldehyde absorption tower is connected to an absorption tail gas treatment device or an incinerator.

[0021] Preferably, the circulating gas dehumidifier is used to remove water from the circulating gas and reduce the concentrations of formaldehyde and methanol in the circulating gas.

[0022] The circulating air dehumidifier can reduce formaldehyde and moisture in the circulating air, thereby reducing side reactions, extending the life of the catalyst, and improving conversion rates. It also requires less chilled water for cooling than traditional absorption towers, reducing chilled water demand by over 50%.

[0023] Preferably, the gas-liquid separator is used to separate the dilute aldehyde entrained in the circulating gas from the circulating gas.

[0024] It can significantly reduce the possibility of dilute formaldehyde entering the circulating gas booster blower inlet pipeline under various working conditions. If dilute formaldehyde enters the pipeline, it will produce polymerized formaldehyde.

[0025] Preferably, the methylal oxidation reactor is a tubular fixed catalyst bed.

[0026] Preferably, a thermal oil electric heater is provided in the bypass between the thermal oil heat exchangers to increase the temperature of the thermal oil.

[0027] Preferably, the formaldehyde absorption tower adopts multi-stage segmented circulation spray absorption;

[0028] On the one hand, it improves the formaldehyde absorption effect, and on the other hand, it controls the temperature distribution in the absorption tower by controlling the temperature of the spray liquid, thereby removing excess heat in the absorption tower.

[0029] Preferably, a bubble cap absorption tray is provided on the top of the formaldehyde absorption tower, and a multi-stage packing bed layer is provided below the bubble cap tray.

[0030] Preferably, the circulating gas dehumidifier uses a chilled water fin heat exchanger to condense the dilute aldehyde, methanol and water in the circulating gas through a cold surface; the dilute aldehyde is separated and sent to a gas-liquid separator.

[0031] On the one hand, it reduces the formaldehyde and moisture content in the circulating gas, which can appropriately reduce useless circulation and thus reduce energy consumption. On the other hand, it can reduce side reactions in the methylal oxidation reactor, improve reaction selectivity and yield, and extend the service life of the catalyst.

[0032] Preferably, the circulating gas and air enter the gas-liquid separator from both sides of the top of the gas-liquid separator, and a partition is provided between the two gases; and a liquid seal is provided at the bottom of the gas-liquid separator.

[0033] Due to various working conditions, there may be a certain amount of dilute aldehyde entrained in the circulating gas. The use of a gas-liquid separator can more thoroughly separate the dilute aldehyde from the circulating gas and prevent the dilute aldehyde from entering the circulating fan inlet pipeline.

[0034] The isolation panels can reduce the amount of dilute formaldehyde volatilized into the fresh air, thereby reducing the total amount of formaldehyde in the circulating air.

[0035] The bottom liquid seal can prevent the circulating gas from short-circuiting at the circulating gas dehumidifier. It can also prevent formaldehyde from polymerizing in the gas-liquid separator under special working conditions.

[0036] In another aspect, the present invention provides a method for oxidizing methylal to produce concentrated formaldehyde, comprising the following steps:

[0037] S1: Air is pressurized by the fresh air blower and enters the gas-liquid separator. After mixing with the circulating gas, it enters the circulating gas pressurizing blower to obtain a circulating mixed gas. The pressurized circulating mixed gas is mixed with the methylal gas from the methylal gasifier in the circulating gas mixer to obtain a reaction circulating gas.

[0038] S2: The reaction circulating gas obtained in step S1 is passed through the reactor inlet and outlet gas heat exchangers, and is heat exchanged with the post-reaction mixed gas after heat energy recovery, and the temperature is raised to 115°C-155°C;

[0039] S3: The reaction circulating gas obtained in step S2 enters each tubular reactor of the methylal oxidation reactor, is heated to 230°C-250°C, enters the molybdenum-chromium-iron catalyst bed, and reacts under the action of the catalyst to obtain a post-reaction mixed gas;

[0040] The reaction temperature in the methylal oxidation reactor is controlled by the gasification temperature of the thermal oil;

[0041] S4: The reaction mixture obtained in step S3 is cooled in two stages through the reactor inlet and outlet heat exchangers, and then enters the formaldehyde absorption tower to absorb formaldehyde through circulating spraying; the distribution of formaldehyde and methanol in the absorption tower is controlled by controlling the circulating spraying temperature;

[0042] S5: The post-reaction mixed gas obtained in step S4 is absorbed in a formaldehyde absorption tower and then divided into two parts. One part is drawn out from the side of the formaldehyde absorption tower as circulating gas; the other part is further absorbed by the multi-layer bubble cap tray on the top of the formaldehyde absorption tower to obtain absorbed tail gas, which is then sent to the absorption tail gas treatment device after pressure control;

[0043] S6: In step S5, the circulating gas dehumidifier condenses and captures moisture and dilute aldehydes in the circulating gas, passes through the gas-liquid separator, separates the dilute aldehydes, mixes them with air, and enters the circulation through the circulating gas pressurized fan.

[0044] Preferably, in step S1, the amount of air added is adjusted according to the oxygen concentration in the circulating mixed gas;

[0045] Preferably, in step S1, the pressure of the gas-liquid separator is 3 KPaG-40 KPaG; further preferably, the pressure of the gas-liquid separator is 3 KPaG-35 KPaG.

[0046] Preferably, in step S1, the air intake pressure at the inlet of the circulating gas pressurizing blower is 3KPaG-40KPaG; further preferably, in step S1, the air intake pressure at the inlet of the circulating gas pressurizing blower is 3KPaG-35KPaG.

[0047] Preferably, in step S2, the temperature is raised to 120°C-150°C.

[0048] Preferably, in step S3, the shell and tube reactor is selected from at least one of DN15, DN20 or DN25; further preferably, in step S3, the shell and tube reactor is DN20.

[0049] Preferably, in step S3, the flow rate of the reaction cycle gas in the tubular reactor is 1.0-5.0 Nm 3 / h / branch tube; Further preferably, in step S3, the flow rate of the reaction cycle gas in the tube reactor is 2.6-2.9 Nm 3 / h / branch tubes.

[0050] Preferably, in step S3, the catalyst filling height in the tubular reactor is 700 mm-1300 mm; further preferably, in step S3, the catalyst filling height in the tubular reactor is 900 mm-1000 mm.

[0051] Preferably, in step S3, the hotspot temperature of the molybdenum-chromium-iron catalyst bed is 310°C-360°C, and the interlocking temperature is 400°C-410°C; further preferably, in step S3, the hotspot temperature of the molybdenum-chromium-iron catalyst bed is 320°C-350°C, and the interlocking temperature is 400°C-405°C.

[0052] Preferably, in step S3, the catalyst molybdenum-chromium-iron catalyst is selected from type A molybdenum-chromium-iron catalyst and / or type B molybdenum-chromium-iron catalyst;

[0053] Preferably, the A-type molybdenum-chromium-iron catalyst comprises the following components in parts by mass:

[0054] 45-75 parts of molybdenum oxide, 20-45 parts of chromium oxide, 5-20 parts of iron oxide, and 3.5-12 parts of metal oxide;

[0055] Further preferably, the A-type molybdenum-chromium-iron catalyst comprises the following components in parts by mass:

[0056] 50-70 parts of molybdenum oxide, 25-40 parts of chromium oxide, 10-20 parts of iron oxide, and 3.5-10 parts of metal oxide;

[0057] The methanol content in the concentrated formaldehyde product prepared by using type A molybdenum-chromium-iron catalyst is ≤0.5wt%.

[0058] Preferably, the metal oxide is at least one selected from the group consisting of oxides of aluminum, titanium, strontium, cobalt, bismuth, and vanadium; further preferably, the metal oxide is at least one selected from the group consisting of oxides of titanium, strontium, and cobalt;

[0059] Preferably, the B-type molybdenum-chromium-iron catalyst comprises the following components in parts by mass:

[0060] 45-75 parts of molybdenum oxide, 5-30 parts of chromium oxide, 5-20 parts of iron oxide, and 3.5-12 parts of metal oxide;

[0061] Further preferably, the B-type molybdenum-chromium-iron catalyst comprises the following components in parts by mass:

[0062] 50-70 parts of molybdenum oxide, 10-30 parts of chromium oxide, 10-20 parts of iron oxide, and 3.5-10 parts of metal oxide;

[0063] The B-type molybdenum-chromium-iron catalyst is used to prepare a concentrated formaldehyde product with a content of 0.5 wt % ≤ methanol ≤ 6 wt %.

[0064] Preferably, the metal oxide is at least one selected from the group consisting of oxides of aluminum, titanium, strontium, cobalt, bismuth, and vanadium; further preferably, the metal oxide is at least one selected from the group consisting of oxides of titanium, strontium, and cobalt;

[0065] Preferably, the shape of the catalyst is selected from cylindrical, annular, spherical, bar, honeycomb, gear or hollow cylindrical; further preferably, the shape of the catalyst is selected from cylindrical and annular.

[0066] More preferably, the catalyst is in the shape of a Raschig ring.

[0067] Preferably, in step S3, the concentration of methylal at the inlet of the methylal oxidation reactor is 2.5 vol%-4.5 vol%;

[0068] Preferably, in step S3, the gasification temperature of the thermal oil is controlled by controlling the gas phase pressure of the thermal oil through a thermal oil heat exchanger, thereby controlling the temperature of the methylal oxidation reactor 3 .

[0069] Preferably, in step S3, the heat transfer oil is selected from at least one of biphenyl-biphenyl ether heat transfer oil and methylnaphthalene.

[0070] Preferably, in step S4, the two-stage cooling is specifically as follows: in the first stage, boiler water is used to exchange heat with the reaction circulating gas obtained in step S3 through the reactor inlet and outlet gas heat exchanger; after the temperature of the reaction circulating gas obtained in step S3 is reduced, heat exchange is performed with the reaction circulating gas from the circulating gas mixer in the second stage of the reactor inlet and outlet gas heat exchanger.

[0071] Preferably, in step S4, the cyclic spraying is a multi-stage filler cyclic spraying, wherein the multi-stage filler is a PE step ring.

[0072] Preferably, in step S4, the circulating spray temperature is controlled by heating the circulating liquid in the kettle of the formaldehyde absorption tower through the concentrated formaldehyde heater in the kettle.

[0073] Preferably, in step S4, the concentration of the absorbed formaldehyde is 60wt%-72wt%.

[0074] Preferably, in step S5, softened water is added to the top of the formaldehyde absorption tower to further absorb formaldehyde gas.

[0075] Preferably, in step S5, the absorption tail gas contains carbon monoxide, methyl formate, and dimethyl ether, which are oxidized by an absorption tail gas treatment device or an incineration system and then meet emission standards.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] 1. The present invention achieves precise reaction temperature control of methylal through rational design of the device structure, control of the reactor inlet temperature, removal of reaction heat within the methylal oxidation reactor, two-stage cooling of the reactor inlet and outlet air heat exchangers, and multi-stage circulating spray temperature control. The conversion rate of methylal catalytic oxidation reaches over 99.5%, and the formaldehyde concentration in concentrated formaldehyde is controlled within a range of 60 wt% to 72 wt% as needed; the concentration of methanol in the concentrated formaldehyde is 0.5 wt% to 6.0 wt%.

[0078] 2. The present invention achieves precise control of methanol concentration through precise temperature control of the formaldehyde absorption tower. In addition, through the spray design of the formaldehyde absorption tower kettle, the scaling problem of concentrated formaldehyde is perfectly solved, and the continuous and stable production of concentrated formaldehyde is achieved.

[0079] 3. The present invention achieves the preparation of high-concentration formaldehyde. During the concentration process, the device of the present invention can reduce the energy consumption of formaldehyde concentration and reduce the production of dilute formaldehyde; there is no need for pressurized distillation of dilute formaldehyde, which reduces energy consumption, reduces investment, and reduces the production of wastewater, thereby significantly reducing carbon emissions.

[0080] 4. The present invention solves the problem of difficult treatment of dilute aldehyde in formaldehyde-related processes. Dilute aldehyde is converted into high-concentration methylal at a very low cost and used as a raw material for generating formaldehyde. The process flow is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 The present invention is a schematic diagram of an apparatus for oxidizing methylal to produce concentrated formaldehyde.

[0082] The markings in the figure are as follows: 1: methylal gasifier; 2: reactor inlet and outlet air heat exchanger; 3: methylal oxidation reactor; 4: formaldehyde absorption tower; 5: circulating gas dehumidifier; 6: gas-liquid separator; 7: circulating gas pressure fan; 8: circulating gas mixer; 9: fresh air fan; 10: boiler water high-level tank; 11: thermal oil heat exchanger; 12: concentrated aldehyde heater; 13: circulating cooler; 14: absorption tail treatment device; 15: methylal unit. DETAILED DESCRIPTION

[0083] In order to make the technical means, creative features, purpose and effect of the present invention easy to understand, the present invention is further illustrated below in conjunction with specific embodiment, but the following embodiment is only a preferred embodiment of the present invention, not all. Based on the embodiment in the embodiment, other embodiments obtained by those skilled in the art without making creative work all fall within the protection scope of the present invention. It is worth noting that the raw materials used in the present invention are all common commercial products, and their source is not specifically limited. The technology and scientific terms used in the embodiment have the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0084] Example device:

[0085] A device for producing concentrated formaldehyde by methylal oxidation method, comprising a methylal gasifier 1; a reactor inlet and outlet air heat exchanger 2; a methylal oxidation reactor 3; a formaldehyde absorption tower 4; a circulating air dehumidifier 5; a gas-liquid separator 6; a circulating air pressure fan 7; a circulating air mixer 8; a fresh air fan 9; a boiler water header tank 10; a thermal oil heat exchanger 11; a concentrated formaldehyde heater 12; a circulating cooler 13; an absorption tail treatment device 14; a methylal unit 15; Figure 1 Connections shown.

[0086] In methylal vaporizer 1, methylal is pumped in from methylal unit 15 and accurately metered before delivery. Steam at -50 to 50 kPa is used to condense liquid from the shell side of methylal vaporizer 1, while non-condensable gas is extracted from the lower portion of the shell side. Within methylal vaporizer 1, the raw methylal is completely converted into methylal gas.

[0087] The reactor inlet and outlet gas heat exchanger 2 is a combined steam generator and gas heat exchanger. The reaction circulating gas first exchanges heat with boiler water in the first section, producing low-pressure steam as a by-product. After completing the first cooling step, it enters the second section of the gas heat exchanger, undergoes heat exchange with the unreacted reaction circulating gas, and is then further cooled before being fed into the formaldehyde absorption tower 4. The unreacted reaction circulating gas then heats up and enters the reactor inlet. This second section of heat exchange is relatively gentle and safe, and will not cause the gas temperature at the reactor inlet to be too high, nor will it cause the temperature of the reacted gas after entering the absorption tower to be too low. Due to the rational design of the heat exchange temperature, the formaldehyde in the reacted circulating mixed gas will not polymerize in the heat exchanger.

[0088] The circulating gas mixer 8 is configured to mix the circulating gas and methylal gas at accurate flow rates sufficiently and evenly in the circulating gas mixer 8. The circulating gas mixer 8 is also configured to be electrostatically grounded.

[0089] The methylal oxidation reactor 3 has a pipeline configuration of 20,000 DN20 tubes, each 1,500 mm long. The shell side uses biphenyl-biphenyl ether heat transfer oil as the heat exchange medium.

[0090] The circulating air dehumidifier 5 is a chilled water fin heat exchanger that uses chilled water as the refrigerant. The dehumidifier's fins capture moisture from the circulating air, simultaneously capturing most of the formaldehyde and methanol. The condensed dilute formaldehyde solution flows by gravity into the gas-liquid separator 6.

[0091] The circulating gas enters the gas-liquid separator 6 from the top, with a small amount of condensate flowing in. Fresh air (air) from the fresh air blower 9 enters from the other side of the top of the gas-liquid separator 6. The fresh air flow rate is fine-tuned based on the oxygen concentration at the outlet of the circulating gas pressurized blower.

[0092] The formaldehyde absorption tower 4 is equipped with 5 layers of random packing corresponding to 5 sections of spray circulation and 13 layers of bubble cap trays on the top. The concentration of concentrated formaldehyde in the bottom of the tower is adjusted by adding desalted water at the top of the tower.

[0093] In the thermal oil heat exchanger 11, the gaseous thermal oil from the shell side of the methylal oxidation reactor 3 enters the lower head of the thermal oil heat exchanger 11, is condensed by the boiler water on the shell side in the tubes, and enters the lower shell side of the methylal oxidation reactor 3, forming a circulation system. The boiler water on the shell side of the thermal oil heat exchanger 13 vaporizes and removes the reaction heat, producing medium-pressure steam as a byproduct.

[0094] Example 1

[0095] Set the parameters as follows:

[0096] The catalyst of the methylal oxidation reactor 3 is a type A molybdenum-chromium-iron catalyst;

[0097] The catalyst formula is:

[0098] 50-70 parts of molybdenum oxide, 25-40 parts of chromium oxide, 10-20 parts of iron oxide, and 3.5-10 parts of metal oxide;

[0099] The metal oxide is a mixture of titanium dioxide, strontium oxide and cobalt oxide, and the mass ratio of titanium dioxide, strontium oxide and cobalt oxide is 1:0.15:0.5;

[0100] The catalyst filling height is 1000mm;

[0101] Raschig ring catalyst (outer diameter φ5±0.2mm, inner diameter φ2±0.2mm, height 4±0.2mm);

[0102] The hot spot temperature of the catalyst bed is 315-360℃, and the interlocking temperature is 405℃.

[0103] Target reaction tube single tube flow rate: 2.0Nm 3 / h / branch tube, 2.4 Nm 3 / h / branch tube, 2.8 Nm 3 / h / branch tube, 3.0 Nm 3 / h / branch tubes.

[0104] Methylal concentration at the reactor inlet: 2.5 vol%, 2.9 vol%, 3.3 vol%, 3.7 vol%, 4.1 vol%, 4.5 vol%.

[0105] Absorption tower target formaldehyde concentration: 60±0.5wt%. Methanol concentration: ≤0.5wt%.

[0106] Methylal raw material: methylal ≥ 98.0wt%.

[0107] Here are the steps:

[0108] S1: Air is pressurized by the fresh air blower 9 and enters the gas-liquid separator 6. After mixing with the circulating gas, it enters the circulating gas pressurizing blower 7 to obtain a circulating mixed gas. The pressurized circulating mixed gas is mixed with the methylal gas from the methylal gasifier 1 in the circulating gas mixer 8 to obtain a reaction circulating gas. The pressure of the gas-liquid separator 6 is 3 kPaG-35 kPaG. The air inlet pressure of the circulating gas pressurizing blower 7 is 3 kPaG-35 kPaG.

[0109] S2: The reaction circulating gas obtained in step S1 passes through the reactor inlet and outlet gas heat exchanger 2, exchanges heat with the post-reaction mixed gas after heat energy recovery, and is heated to 120°C-150°C;

[0110] S3: The reaction circulating gas obtained in step S2 enters each tubular reactor (DN20) of the methylal oxidation reactor 3, is heated to 235°C-245°C, enters the molybdenum-chromium-iron catalyst bed, and reacts under the action of the catalyst to obtain a post-reaction mixed gas;

[0111] The reaction temperature in the methylal oxidation reactor 3 is controlled by the thermal oil vaporization temperature; the thermal oil vaporization temperature is controlled by the thermal oil heat exchanger 11 to control the thermal oil gas phase pressure. This in turn controls the temperature of the methylal oxidation reactor 3;

[0112] The heat transfer oil is selected from at least one of biphenyl-biphenyl ether heat transfer oil and methylnaphthalene;

[0113] S4: The post-reaction mixed gas obtained in step S3 is cooled in two stages through the reactor inlet and outlet gas heat exchangers 2, and then enters the formaldehyde absorption tower 4 where it is sprayed by a multi-stage packing for cyclic absorption of formaldehyde; the multi-stage packing is a PE step ring; the formaldehyde and methanol concentration distribution in the absorption tower is controlled by controlling the circulating spray temperature; the circulating spray temperature is controlled by heating the circulating liquid in the bottom of the formaldehyde absorption tower 4 through the concentrated formaldehyde heater 12 in the bottom of the tower;

[0114] The two-stage cooling process is as follows: in the first stage, the boiler water is used to exchange heat with the reaction circulating gas obtained in step S3 through the reactor inlet and outlet gas heat exchanger 2. After the temperature of the reaction circulating gas obtained in step S3 is reduced, the reaction circulating gas is then heat exchanged with the reaction circulating gas from the circulating gas mixer 8 in the second stage of the reactor inlet and outlet gas heat exchanger 2;

[0115] S5: A portion of the post-reaction mixed gas obtained in step S4 is introduced from the side of the formaldehyde absorption tower 4 into the circulating gas dehumidifier 5 for absorption to obtain circulating gas; the other portion is further absorbed by the multi-layer bubble tower tray on the top of the formaldehyde absorption tower to obtain absorbed tail gas, which is then sent to the absorption tail gas treatment device 14 after pressure control; softened water is added to the top of the formaldehyde absorption tower 4 to further absorb formaldehyde gas. The absorbed tail gas contains carbon monoxide, methyl formate, and dimethyl ether, which are oxidized by the ECS reactor or the incineration system and then discharged in compliance with the emission standards.

[0116] S6: In step S5, the circulating gas dehumidifier 5 condenses and captures moisture and formaldehyde in the circulating gas to obtain dilute formaldehyde, which is separated by the gas-liquid separator 6 and then mixed with air and enters the circulation through the circulating gas pressurized fan 7.

[0117] Table 1. Collection and operation data 1

[0118]

[0119] Table 2. Collection operation data 2

[0120]

[0121] Table 3. Collection operation data 3

[0122]

[0123] Note: “ / ” means not running.

[0124] Table 4. Collection of running data 4

[0125]

[0126] Example 2

[0127] Set the parameters as follows:

[0128] The catalyst of the methylal oxidation reactor 3 is a B-type molybdenum-chromium-iron catalyst;

[0129] The catalyst formula is: 50-70 parts of molybdenum oxide, 10-30 parts of chromium oxide, 10-20 parts of iron oxide, and 3.5-10 parts of metal oxide;

[0130] The metal oxide is a mixture of titanium dioxide, strontium oxide and cobalt oxide, and the mass ratio of titanium dioxide, strontium oxide and cobalt oxide is 1:0.15:0.5;

[0131] The catalyst filling height is 1000mm;

[0132] Raschig ring catalyst (outer diameter φ5±0.2mm, inner diameter φ2±0.2mm, height 4±0.2mm);

[0133] The hot spot temperature of the catalyst bed is 315-350℃, and the interlocking temperature is 405℃.

[0134] Target reaction tube single tube flow rate 2.8 Nm 3 / h / branch tubes.

[0135] Methylal concentration at the reactor inlet: 3.7 vol%, 4.1 vol%.

[0136] Absorption tower target formaldehyde concentration: 69±1.0wt%. Methanol concentration: ≤6.0wt%.

[0137] Methylal raw material: methylal ≥ 98.0wt%.

[0138] The operation steps are the same as those in Example 1.

[0139] Table 5. Collection of running data 5

[0140]

[0141] Note: “ / ” means not running.

[0142] According to the data in Table 1-Table 5, at 2.8±0.05Nm 3 / h flow rate, the best effect is achieved when the methylal concentration is controlled between 4.1%±0.05%; the present invention realizes precise reaction temperature control of methylal through reasonable design of the device structure, through the reactor inlet temperature, the removal control of the reaction heat in the methylal oxidation reactor, the two-stage cooling of the reactor inlet and outlet air heat exchanger, and the multi-stage circulation spray temperature control; the conversion rate of methylal catalytic oxidation reaches more than 99.5%, and the formaldehyde concentration in the concentrated formaldehyde is controlled within 60wt%-72wt% as needed; the concentration of methanol in the concentrated formaldehyde is 0.5wt%-6.0wt%.

[0143] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A device for producing concentrated formaldehyde by oxidizing methylal, characterized in that: The invention comprises the following: a methylal unit (15), a methylal gasifier (1), a fresh air blower (9), a heat transfer oil heat exchanger (11), a concentrated aldehyde heater (12), a circulating gas pressurizing blower (7), a circulating gas mixer (8), a reactor inlet and outlet air heat exchanger (2), a methylal oxidation reactor (3), a formaldehyde absorption tower (4), a circulating gas dehumidifier (5), a gas-liquid separator (6), and an absorption tail gas treatment device (14); The circulating gas mixer (8) is connected upstream to the methylal gasifier (1); The gas-liquid separator (6) is connected upstream to a fresh air blower (9); The methylal oxidation reactor (3) is connected to a thermal oil heat exchanger (11); The formaldehyde absorption tower (4) is connected to a concentrated formaldehyde heater (12); The circulating gas dehumidifier (5) is used to remove water from the circulating gas, thereby reducing the concentrations of formaldehyde and methanol in the circulating gas; The gas-liquid separator (6) is used to separate the dilute aldehydes entrained in the circulating gas; The circulating gas dehumidifier (5) uses a chilled water fin heat exchanger to condense the dilute aldehyde, methanol and water in the circulating gas through the cold surface; the dilute aldehyde is separated and sent to the gas-liquid separator (6); The circulating gas and air enter from both sides of the top of the gas-liquid separator (6), with a partition provided between the two gases; a liquid seal is provided at the bottom of the gas-liquid separator; The method for preparing concentrated formaldehyde using the device comprises the following steps: S1: Air is pressurized by the fresh air blower (9) and enters the gas-liquid separator (6), where it is mixed with the circulating gas and then enters the circulating gas pressurizing blower (7) to obtain a circulating mixed gas; the pressurized circulating mixed gas is mixed with the methylal gas from the methylal gasifier (1) in the circulating gas mixer (8) to obtain a reaction circulating gas; S2: The reaction circulating gas obtained in step S1 passes through the reactor inlet and outlet gas heat exchanger (2), exchanges heat with the post-reaction mixed gas after heat energy recovery, and is heated to 115°C-155°C; S3: The reaction circulating gas obtained in step S2 enters each tubular reactor of the methylal oxidation reactor (3), is heated to 230°C-250°C, enters the molybdenum-chromium-iron catalyst bed, and reacts under the action of the catalyst to obtain a post-reaction mixed gas; The reaction temperature in the methylal oxidation reactor (3) is controlled by the gasification temperature of the thermal oil; The molybdenum-chromium-iron catalyst is a type A molybdenum-chromium-iron catalyst, and the catalyst formula is: 50-70 parts of molybdenum oxide, 25-40 parts of chromium oxide, 10-20 parts of iron oxide, and 3.5-10 parts of metal oxide; The metal oxide is a mixture of titanium dioxide, strontium oxide and cobalt oxide, and the mass ratio of titanium dioxide, strontium oxide and cobalt oxide is 1:0.15:0.5; The filling height of the molybdenum-chromium-iron catalyst is 1000 mm; The flow rate of the reaction cycle gas in the tubular reactor is 2.0, 2.4, 2.8, 3.0 Nm 3 / h / branch tube; When the flow rate of the reaction cycle gas in the tubular reactor is 2.8 Nm 3 / h / branch tube, when the methylal concentration at the reactor inlet is 3.7vol%, the hotspot temperature of the molybdenum-chromium-iron catalyst bed is 329.2℃, and the hotspot position is 600mm; when the flow rate of the reaction cycle gas in the tube reactor is 2.8Nm 3 / h / branched tube, when the methylal concentration at the reactor inlet is 4.1 vol%, the hotspot temperature of the molybdenum-chromium-iron catalyst bed is 331.2°C, and the hotspot position is 650 mm; S4: The reaction mixture obtained in step S3 is cooled in two stages by the reactor inlet and outlet heat exchangers (2), and then enters the formaldehyde absorption tower (4) to absorb formaldehyde through circulating spraying; the distribution of formaldehyde and methanol in the absorption tower is controlled by controlling the circulating spraying temperature; S5: The reaction mixture obtained in step S4 is absorbed by the formaldehyde absorption tower (4) and then divided into two parts. One part is drawn out from the side of the formaldehyde absorption tower (4) as circulating gas; the other part is further absorbed by the multi-layer bubble cap tray at the top of the formaldehyde absorption tower (4) to obtain the absorbed tail gas, which is then pressure-controlled and sent to the absorption tail gas treatment device (14); S6: In step S5, the circulating gas dehumidifier (5) condenses and captures the moisture and dilute aldehyde in the circulating gas, passes through the gas-liquid separator (6), separates the dilute aldehyde, mixes it with air, and enters the circulation through the circulating gas pressurizing fan (7).

2. The device according to claim 1, characterized in that The methylal gasifier (1) is connected to low-grade steam; The reactor inlet and outlet air heat exchangers (2) are connected to the boiler water high level tank (10) in the first stage; The formaldehyde absorption tower (4) is connected to a circulating cooler (13); The concentrated aldehyde heater (12) is connected to low-grade steam; The pipeline of the methylal oxidation reactor (3) is connected to a thermal oil electric heater through a bypass; The tail gas from the top of the formaldehyde absorption tower (4) is connected to an absorption tail gas treatment device (14) or an incinerator.

3. A method for preparing concentrated formaldehyde by oxidizing methylal, characterized in that: Using the device according to any one of claims 1 to 2, comprising the following steps: S1: Air is pressurized by the fresh air blower (9) and enters the gas-liquid separator (6), where it is mixed with the circulating gas and then enters the circulating gas pressurizing blower (7) to obtain a circulating mixed gas; the pressurized circulating mixed gas is mixed with the methylal gas from the methylal gasifier (1) in the circulating gas mixer (8) to obtain a reaction circulating gas; S2: The reaction circulating gas obtained in step S1 passes through the reactor inlet and outlet gas heat exchanger (2), exchanges heat with the post-reaction mixed gas after heat energy recovery, and is heated to 115°C-155°C; S3: The reaction circulating gas obtained in step S2 enters each tubular reactor of the methylal oxidation reactor (3), is heated to 230°C-250°C, enters the molybdenum-chromium-iron catalyst bed, and reacts under the action of the catalyst to obtain a post-reaction mixed gas; The reaction temperature in the methylal oxidation reactor (3) is controlled by the gasification temperature of the thermal oil; S4: The reaction mixture obtained in step S3 is cooled in two stages by the reactor inlet and outlet heat exchangers (2), and then enters the formaldehyde absorption tower (4) to absorb formaldehyde through circulating spraying; the distribution of formaldehyde and methanol in the absorption tower is controlled by controlling the circulating spraying temperature; S5: The reaction mixture obtained in step S4 is absorbed by the formaldehyde absorption tower (4) and then divided into two parts. One part is drawn out from the side of the formaldehyde absorption tower (4) as circulating gas; the other part is further absorbed by the multi-layer bubble cap tray at the top of the formaldehyde absorption tower (4) to obtain the absorbed tail gas, which is then pressure-controlled and sent to the absorption tail gas treatment device (14); S6: In step S5, the circulating gas dehumidifier (5) condenses and captures the moisture and dilute aldehyde in the circulating gas, passes through the gas-liquid separator (6), separates the dilute aldehyde, mixes it with air, and enters the circulation through the circulating gas pressurizing fan (7).

4. The method according to claim 3, characterized in that In step S1, the pressure of the gas-liquid separator (6) is 3KPaG-40KPaG.

5. The method according to claim 3, characterized in that In step S1, the inlet pressure of the circulating air pressure blower (7) is 3KPaG-40KPaG.

6. The method according to claim 3, characterized in that In step S3, the gasification temperature of the heat transfer oil is controlled by the heat transfer oil heat exchanger (11), and the gas phase pressure of the heat transfer oil is controlled, thereby controlling the temperature of the methylal oxidation reactor (3).

7. The method according to claim 3, characterized in that In step S3, the heat transfer oil is selected from at least one of biphenyl-biphenyl ether heat transfer oil and methylnaphthalene.

8. The method according to claim 3, characterized in that In step S4, the two-stage cooling is specifically as follows: in the first stage, boiler water is used to exchange heat with the reaction circulating gas obtained in step S3 through the reactor inlet and outlet gas heat exchanger (2); after the temperature of the reaction circulating gas obtained in step S3 is reduced, heat exchange is performed with the reaction circulating gas from the circulating gas mixer (8) in the second stage of the reactor inlet and outlet gas heat exchanger (2).

9. The method according to claim 3, characterized in that In step S4, the cyclic spraying is multi-stage filler cyclic spraying; the multi-stage filler is PE stepped ring.

10. The method according to claim 3, characterized in that In step S4, the circulating spray temperature is controlled by heating the circulating liquid in the bottom of the formaldehyde absorption tower (4) through the concentrated formaldehyde heater (12) in the bottom of the tower.

11. The method according to claim 3, characterized in that In step S4, the concentration of the absorbed formaldehyde is 60wt%-72wt%.

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