Device for preparing anhydrous formaldehyde solution

Abstract

The utility model provides a device for preparing an anhydrous formaldehyde solution, which relates to the technical field of chemical synthesis and comprises a dehydrogenation reactor, a liquefaction tower, a gas-liquid separation tower, an absorption tower and a desorption tower which are sequentially connected according to a feeding sequence, wherein a catalytic reaction section, a liquefaction tower, a gas-liquid separation tower and an absorption tower are arranged in the dehydrogenation reactor, and a separation filler section is arranged in the desorption tower; the device for preparing the anhydrous formaldehyde solution, provided by the utility model, has the characteristics of reasonable structure and convenience in operation, and solves the problem of source of anhydrous formaldehyde serving as a raw material for synthesizing polyoxymethylene dimethyl ether; the technical effects that the flowable anhydrous formaldehyde solution can be conveniently obtained at low cost, and the method is safe, environmentally friendly, energy-saving and suitable for industrial production are achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of chemical synthesis, in particular to a device for preparing anhydrous formaldehyde solution. Background Art

[0002] Polyoxymethylene dimethyl ether, also known as polyformaldehyde dimethyl ether or polymethylene dimethyl ether, with the English name Polyoxymethylene dimethylethers, abbreviated as DMMn or PODE, is a class of low molecular weight acetal polymers with dimethoxymethane as the parent body and methyleneoxy as the main chain, and its general formula is: CH3O(CH2O)nCH3. Among them, polyoxymethylene dimethyl ether with a polymerization degree of 3-8, abbreviated as DMM3-8, is used as a blending component for clean diesel. Its physical properties are similar to those of diesel, and no modification is required for the vehicle engine fuel supply system when blended into diesel; its cetane number is as high as 76, oxygen content is 47% - 50%, sulfur-free and aromatic-free. When blended 0.1% - 20% in diesel, it can significantly reduce the cold filter plugging point of diesel, improve the combustion quality of diesel in the engine, and increase the thermal efficiency.

[0003] At the same time, DMM2, DMM3, DMM4, DMM5 and their mixtures are also a class of solvents with extremely strong solubility, and are applied to paints, coatings, inks, adhesives, cleaning agents, electrolyte solvents, etc.; DMMn has a high oxygen content and a low carbon content (42 - 45%), playing a positive environmental protection substitution role in the solvent field.

[0004] Polyoxymethylene dimethyl ether is usually prepared by the reaction of methanol or methylal with trioxymethylene or paraformaldehyde in the presence of an acidic catalyst. The basic reaction equation is as follows:

[0005]

[0006] The process of catalytic synthesis of polyoxymethylene dimethyl ether by an acidic catalyst is an equilibrium reaction, and the content of the effective component (DMM3-8) is relatively low. Generally, the content of DMM3-8 in the synthesis liquid is below 40%. However, the presence of a small amount of water promotes the reverse shift of the equilibrium, and the influence is relatively large, resulting in a large amount of methanol, formaldehyde, paraformaldehyde and hemiacetal remaining in the reaction liquid, and the content of the effective component is even lower, causing difficulties in the purification and low-cost preparation of polyoxymethylene dimethyl ether; because the equilibrium conversion rate is relatively low, the recycled materials separated during product purification must be recycled. The water therein is combined with formaldehyde, paraformaldehyde and hemiacetal, and it is difficult to remove by conventional methods.

[0007] Therefore, people came up with the idea of using anhydrous formaldehyde or formaldehyde with a low water content, which led to the use of trioxane, paraformaldehyde, to prepare anhydrous or low-moisture gaseous formaldehyde, or the idea of using a relatively concentrated aqueous formaldehyde solution for synthesis and removing the water in the system during the synthesis process.

[0008] However, trioxane is synthesized from aqueous formaldehyde solution catalyzed by sulfuric acid. In its production process, there is a large amount of reflux in the presence of water. The heat of vaporization of water is relatively large, resulting in high energy consumption. Solvent extraction and dehydration are also required, and its synthesis cost is relatively high. Also, because trioxane has a relatively high melting point (61 °C), it is prone to sublimation and can easily cause pipeline blockage, leading to dangerous accidents, etc. At the same time, during the storage and transportation of trioxane, once strong acidic substances are mixed in, it will polymerize to form high-molecular polymers, rendering the equipment useless.

[0009] At the same time, paraformaldehyde is obtained by dehydrating an aqueous formaldehyde solution to less than 15% water content under vacuum conditions and then polymerizing and solidifying it, and then through processes such as granulation or pulverization and drying to obtain a solid form. Although the manufacturing cost is somewhat reduced, when it is further used as a reactant, due to its insoluble and infusible properties, its reaction activity is relatively low, making it inconvenient for feeding from synthesis to application during continuous production. In addition, formaldehyde has a strong odor and high toxicity, which is harmful to the health of workers. Moreover, despite drying, its water content is still difficult to reach below 6%, which still has a great impact on the equilibrium reaction of polyoxymethylene dimethyl ether; in the subsequent continuous production process, it has a great impact on the effective conversion rate of formaldehyde, resulting in a large waste of resources.

[0010] There are also reports in China of using a relatively high-concentration aqueous formaldehyde solution (about 20% water content) to react with methanol or methylal to prepare polyoxymethylene dimethyl ether (DMM3-8). Although theoretically, the process is smooth and easy to operate, there are problems such as difficult dehydration of the synthesis liquid, very low conversion rate, a large amount of residual formaldehyde, and difficult separation. Therefore, special synthesis methods such as reactive distillation must be used, but the energy consumption is still relatively high.

[0011] Chinese patents 201510128377.X and 201610147992.X disclose that gaseous formaldehyde and methylal undergo a catalytic reaction in the presence of a catalyst to prepare a DMMn synthesis liquid, and then DMM3-8 is obtained after treatment and separation; however, in this patent, the method for preparing gaseous formaldehyde uses a monohydric alcohol such as isobutanol as an adjuvant. This adjuvant has a relatively low boiling point and is easy to enter the synthesis liquid and the finished product along with formaldehyde. At the same time, this type of adjuvant has a relatively high price, which is not conducive to industrialization; more importantly, after this adjuvant forms a hemiacetal, its water solubility increases, making it very difficult to form a layer with water. Moreover, during its subsequent distillation and dehydration process, due to the influence of the equilibrium, the re-formed auxiliary additive will be distilled out and mixed into the dilute formaldehyde solution.

[0012] Chinese patent 201610076437.2 discloses the use of methanol or methylal in an oxidation reactor to produce formaldehyde synthesis gas through air oxidation; the prepared formaldehyde synthesis gas is then passed into a cooler to be cooled to 20-99°C, and then enters a gas-water separator to remove condensed water to obtain formaldehyde gas. Facts have proved that the formaldehyde gas formed by oxidizing methanol contains about 30% of generated water, and the water content is even higher when the steam added with methanol is added. When the temperature is reduced to 20-99°C, formaldehyde hydrate (methylene glycol) is quickly formed and liquefied, or polymerization reaction occurs and liquefied or solidified. It is difficult to obtain ideal gaseous anhydrous formaldehyde, which is not conducive to industrialization.

[0013] Other conventional methods for preparing anhydrous gaseous formaldehyde include: 1. Heating and depolymerizing polyformaldehyde to prepare gaseous formaldehyde. However, the bound water content of polyformaldehyde itself is about 6%, which greatly affects the yield of DMMn synthesis and the further recycling of intermediate products. Not only is the preparation of solid polyformaldehyde relatively complicated, but further feeding and transportation are not conducive to large-scale and continuous large-scale production, and there are major safety hazards; 2. Triformaldehyde is heated and decomposed and gasified under the action of an acidic catalyst. In this way, triformaldehyde that has not had time to decompose will be vaporized with the gaseous formaldehyde, which is easy to cause blockage of the transportation pipeline. In addition, the cost of triformaldehyde is relatively high, which is not conducive to industrialization.

[0014] Therefore, the presence of moisture is the biggest obstacle to the synthesis, separation and recycling of DMMn. In order to provide a low-cost anhydrous formaldehyde solution that is inexpensive, easy to prepare and easy to use for the preparation of DMMn, after a lot of theoretical and experimental research, it was determined to start with the preparation of formaldehyde, prepare formaldehyde through dehydrogenation of methanol, and further dissolve it in methanol to form an anhydrous formaldehyde methanol solution; and prepare it through a device including a dehydrogenation reactor, a liquefaction tower, a gas-liquid separation tower, a spray absorption tower, and a decomposition tower. Summary of the invention

[0015] The utility model aims to provide a device for preparing anhydrous formaldehyde solution, so as to solve the problem of the source of anhydrous formaldehyde raw materials in the existing polyoxymethylene dimethyl ether synthesis technology.

[0016] Solution: The utility model provides a device for preparing anhydrous formaldehyde solution, which comprises a dehydrogenation reactor, a liquefaction tower, a gas-liquid separation tower, a spray absorption tower, and a desorption tower which are connected in sequence according to the feeding order;

[0017] The dehydrogenation reactor is provided with a synthesis gas outlet, a catalyst packing section, and a gaseous methanol inlet from top to bottom;

[0018] The catalyst packing section of the dehydrogenation reactor is provided with a tubular catalyst packing tube;

[0019] A heater is provided in front of the inlet of the dehydrogenation reactor;

[0020] A heat exchanger is provided in front of the inlet of the heater;

[0021] The syngas outlet of the dehydrogenation reactor is connected to the methanol dehydrogenation syngas gas-phase feed pipe of the liquefaction tower through a heat exchanger;

[0022] The liquefaction tower is provided with a rectifying section, a distributor, a stripping section and a heater from top to bottom;

[0023] The methanol dehydrogenation syngas gas-phase feed pipe is provided at the distributor of the liquefaction tower for feeding the methanol dehydrogenation syngas gas-phase;

[0024] A first reflux device is provided at the top of the liquefaction tower;

[0025] The first reflux device includes a high-temperature methanol and hydrogen mixture condenser, an overflow tank, a low-temperature methanol and hydrogen mixture discharge pipe and a methanol reflux pipe;

[0026] The bottom of the overflow tank is connected to the reflux port of the liquefaction tower through a methanol reflux pipe;

[0027] The low-temperature methanol and hydrogen mixture discharge pipe is used to discharge the low-temperature methanol and hydrogen mixture to the gas-liquid separation tower;

[0028] A gas-phase circulation device is provided at the top of the liquefaction tower;

[0029] The gas-phase circulation device includes a gas-phase delivery pipe and a circulation fan;

[0030] An anhydrous formaldehyde solution discharge pipe is provided at the bottom of the liquefaction tower;

[0031] The gas-liquid separation tower is provided with a reflux condenser, a packing device, a distributor, a stripping section and a heater from top to bottom;

[0032] The packing device of the gas-liquid separation tower is provided with tower packing;

[0033] The low-temperature methanol and hydrogen mixture feed pipe is provided at the distributor of the gas-liquid separation tower for feeding the low-temperature methanol and hydrogen mixture;

[0034] A methanol discharge pipe is provided at the bottom of the gas-liquid separation tower;

[0035] The spray absorption tower is provided with a hydrogen discharge pipe, a reflux condenser, a spray device, a packing device, a distributor and a heat exchanger from top to bottom;

[0036] The packing device of the spray absorption tower is provided with tower packing;

[0037] An absorbent feed pipe is provided at the upper distributor of the spray absorption tower for feeding the absorbent.

[0038] A crude hydrogen feed pipe is provided at the lower distributor of the spray absorption tower for feeding crude hydrogen.

[0039] A crude absorbent discharge pipe is provided at the bottom of the spray absorption tower.

[0040] The stripping tower is provided with a rectifying section, a distributor, a stripping section, and a heater from top to bottom.

[0041] A crude absorbent feed pipe is provided on the distributor of the stripping tower for feeding crude absorbent.

[0042] A second reflux device is provided at the top of the stripping tower.

[0043] The second reflux device includes a methanol condenser.

[0044] The methanol condenser is connected to the reflux port of the stripping tower through a methanol reflux pipe.

[0045] The methanol condenser is further provided with a methanol discharge pipe for withdrawing the recovered methanol.

[0046] An absorbent discharge pipe is provided at the bottom of the stripping tower.

[0047] The absorbent discharge pipe is connected to the upper distributor of the spray absorption tower.

[0048] Furthermore, the tubular catalyst loading pipes in the catalyst packing section of the dehydrogenation reactor are used for packing dehydrogenation catalyst.

[0049] Compared with the existing device for preparing formaldehyde raw materials for synthesizing polyoxymethylene dimethyl ethers, the present utility model has the following advantages:

[0050] The device for preparing anhydrous formaldehyde solution provided by the present utility model has the characteristics of reasonable structure, low operating pressure, convenience and flexibility, easy separation of formaldehyde solution, low energy consumption, etc., solves the problem of the source of anhydrous formaldehyde as the raw material for synthesizing polyoxymethylene dimethyl ethers, and achieves the technical effects of being able to conveniently and low-cost obtain a flowable anhydrous formaldehyde solution, and being safe, environmentally friendly, energy-saving, and suitable for continuous and automated production. Description of the Drawings

[0051] In order to more clearly illustrate the specific embodiments of the present utility model or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the drawings of the present utility model.

[0052] Figure 1 Schematic diagram of an apparatus for preparing anhydrous formaldehyde solution according to the present utility model;

[0053] Illustration: 1 - dehydrogenation reactor; 2 - liquefaction tower; 3 - gas - liquid separation tower; 4 - spray absorption tower; 5 - stripping tower; 6 - condenser; 7 - reflux condenser; 8 - reflux condenser; 9 - methanol condenser; 10 - catalyst packing section; 11 - rectifying section of liquefaction tower; 12 - stripping section of liquefaction tower; 13 - packing device of gas - liquid separation tower; 14 - stripping section of gas - liquid separation tower; 15 - packing device of spray absorption tower; 16 - rectifying section of stripping tower; 17 - stripping section of stripping tower; 18 - reflux port of liquefaction tower; 19 - reflux port of stripping tower; 20 - gaseous methanol inlet of dehydrogenation reactor; 21 - gas - phase feed pipe for methanol dehydrogenation synthesis gas; 22 - feed pipe for low - temperature methanol and hydrogen mixture; 23 - feed pipe for crude hydrogen; 24 - absorbent feed pipe; 25 - feed pipe for crude absorbent; 26 - synthesis gas outlet of dehydrogenation reactor; 27 - discharge pipe for anhydrous formaldehyde solution; 28 - discharge pipe for methanol; 29 - discharge pipe for crude absorbent; 30 - discharge pipe for absorbent; 31 - heater; 32 - heater of liquefaction tower; 33 - heater of gas - liquid separation tower; 34 - heat exchanger of spray absorption tower; 35 - heater of stripping tower; 36 - hydrogen discharge pipe; 37 - discharge pipe for recycled methanol; 38 - heat exchanger; 39 - circulation fan. Detailed implementation manners

[0054] Next, the technical solutions of the present utility model will be clearly and completely described in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present utility model, rather than all of them. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present utility model.

[0055] Detailed implementation manners: As Figure 1 shown, the present utility model provides an apparatus for preparing anhydrous formaldehyde solution, which, in the feeding order, includes a dehydrogenation reactor, a liquefaction tower, a gas - liquid separation tower, a spray absorption tower, and a stripping tower connected in sequence;

[0056] Among them, the dehydrogenation reactor is provided with a synthesis gas outlet, a catalyst packing section, and a gaseous methanol inlet from top to bottom;

[0057] The catalyst packing section of the dehydrogenation reactor is provided with a shell - and - tube catalyst loading tube;

[0058] A heater is provided in front of the inlet of the dehydrogenation reactor;

[0059] A heat exchanger is provided in front of the inlet of the heater;

[0060] The syngas outlet of the dehydrogenation reactor is connected to the methanol dehydrogenation syngas gas-phase feed pipe of the liquefaction tower through a heat exchanger;

[0061] The liquefaction tower is provided with a rectifying section, a distributor, a stripping section and a heater from top to bottom;

[0062] The methanol dehydrogenation syngas gas-phase feed pipe is arranged at the distributor of the liquefaction tower for feeding the methanol dehydrogenation syngas gas-phase;

[0063] The top of the liquefaction tower is provided with a first reflux device;

[0064] The first reflux device includes a high-temperature methanol and hydrogen mixture condenser, an overflow tank, a low-temperature methanol and hydrogen mixture discharge pipe and a methanol reflux pipe;

[0065] The bottom of the overflow tank is connected to the reflux port of the liquefaction tower through the methanol reflux pipe;

[0066] The low-temperature methanol and hydrogen mixture discharge pipe is used to discharge the low-temperature methanol and hydrogen mixture to the gas-liquid separation tower;

[0067] The top of the liquefaction tower is provided with a gas-phase circulation device;

[0068] The gas-phase circulation device includes a gas-phase delivery pipe and a circulation fan;

[0069] The bottom of the liquefaction tower is provided with an anhydrous formaldehyde solution discharge pipe;

[0070] The gas-liquid separation tower is provided with a reflux condenser, a packing device, a distributor, a stripping section and a heater from top to bottom;

[0071] The packing device of the gas-liquid separation tower is provided with tower packing;

[0072] The low-temperature methanol and hydrogen mixture feed pipe is arranged at the distributor of the gas-liquid separation tower for feeding the low-temperature methanol and hydrogen mixture;

[0073] The bottom of the gas-liquid separation tower is provided with a methanol discharge pipe;

[0074] The spray absorption tower is provided with a hydrogen discharge pipe, a reflux condenser, a spray device, a packing device, a distributor and a heat exchanger from top to bottom;

[0075] The packing device of the spray absorption tower is provided with tower packing;

[0076] The absorbent feed pipe is arranged at the upper distributor of the spray absorption tower for feeding the absorbent;

[0077] The crude hydrogen feed pipe is arranged at the lower distributor of the spray absorption tower for feeding the crude hydrogen;

[0078] The bottom of the spray absorption tower is provided with a crude absorbent discharge pipe;

[0079] The analytical column is provided with a rectifying section, a distributor, a stripping section and a heater from top to bottom;

[0080] The distributor of the analytical column is provided with a crude absorbent feed pipe for feeding the crude absorbent;

[0081] The top of the analytical column is provided with a second reflux device;

[0082] The second reflux device includes a methanol condenser;

[0083] The methanol condenser is communicated with the reflux port of the analytical column through a methanol reflux pipe;

[0084] The methanol condenser is also provided with a methanol discharge pipe for discharging the recovered methanol;

[0085] The bottom of the analytical column is provided with an absorbent discharge pipe;

[0086] The absorbent discharge pipe is connected to the upper distributor of the spray absorption column.

[0087] In a preferred embodiment, the dehydrogenation catalyst is filled in the tubular catalyst loading pipes of the catalyst packing section of the dehydrogenation reactor of the present utility model.

[0088] A typical device for preparing anhydrous formaldehyde solution is as Figure 1 shown, including:

[0089] Dehydrogenation reactor 1; liquefaction tower 2; gas-liquid separation tower 3; spray absorption tower 4; analytical column 5; condenser 6; reflux condenser 7; reflux condenser 8; methanol condenser 9; catalyst packing section 10; rectifying section of liquefaction tower 11; stripping section of liquefaction tower 12; packing device of gas-liquid separation tower 13; stripping section of gas-liquid separation tower 14; packing device of spray absorption tower 15; rectifying section of analytical column 16; stripping section of analytical column 17; reflux port of liquefaction tower 18; reflux port of analytical column 19; gaseous methanol inlet of dehydrogenation reactor 20; methanol dehydrogenation synthesis gas gas-phase feed pipe 21; low-temperature methanol and hydrogen mixture feed pipe 22; crude hydrogen feed pipe 23; absorbent feed pipe 24; crude absorbent feed pipe 25; synthesis gas outlet of dehydrogenation reactor 26; anhydrous formaldehyde solution discharge pipe 27; methanol discharge pipe 28; crude absorbent discharge pipe 29; absorbent discharge pipe 30; heater 31; liquefaction tower heater 32; gas-liquid separation tower heater 33; spray absorption tower heat exchanger 34; analytical column heater 35; hydrogen discharge pipe 36; recovered methanol discharge pipe 37; heat exchanger 38; circulation fan 39.

[0090] Specifically, the dehydrogenation reactor 1 is provided with a syngas outlet 26, a catalyst packing section 10, and a gaseous methanol inlet 20 from top to bottom; the catalyst packing section 10 of the dehydrogenation reactor is provided with tube-sheet type catalyst loading tubes; a heater 31 is provided in front of the inlet of the dehydrogenation reactor; a heat exchanger 38 is provided in front of the inlet of the heater 31; the syngas outlet 26 of the dehydrogenation reactor 1 is connected to the methanol dehydrogenation syngas gas-phase feed pipe 21 of the liquefaction tower 2 through the heat exchanger 38; the tube-sheet type catalyst loading tubes in the catalyst packing section 10 of the dehydrogenation reactor 1 are used for packing dehydrogenation catalysts, and a heat transfer medium is passed outside the tube-sheet type catalyst loading tubes;

[0091] The liquefaction tower 2 is provided with a rectifying section 11, a distributor, a stripping section 12, and a heater 32 from top to bottom; a methanol dehydrogenation syngas gas-phase feed pipe 21 is provided at the distributor of the liquefaction tower for feeding methanol dehydrogenation syngas gas-phase; a first reflux device is provided at the top of the liquefaction tower; the reflux device includes a high-temperature methanol and hydrogen mixture condenser 6, an overflow tank, a low-temperature methanol and hydrogen mixture discharge pipe, and a methanol reflux pipe; the bottom of the overflow tank is connected to the reflux port 18 of the liquefaction tower through the methanol reflux pipe; the low-temperature methanol and hydrogen mixture discharge pipe is used for discharging the low-temperature methanol and hydrogen mixture to the low-temperature methanol and hydrogen mixture feed pipe 22 of the gas-liquid separation tower 3; a gas-phase circulation device is provided at the top of the liquefaction tower 2, and the gas-phase circulation device includes a gas-phase transfer pipe and a circulation fan 39. Part of the high-temperature methanol and hydrogen mixture gas phase returns to the heat exchanger 38 through the gas-phase transfer pipe and the circulation fan 39 and participates in the feed after being heated; and an anhydrous formaldehyde solution discharge pipe 27 is provided at the bottom of the liquefaction tower 1;

[0092] The gas-liquid separation tower 3 is provided with a reflux condenser 7, a packing device 13, a distributor, a stripping section 14, and a heater 33 from top to bottom; and the packing device of the gas-liquid separation tower is provided with tower packings;

[0093] A low-temperature methanol and hydrogen mixture feed pipe 22 is provided at the distributor of the gas-liquid separation tower for feeding the low-temperature methanol and hydrogen mixture; a methanol discharge pipe 28 is provided at the bottom of the gas-liquid separation tower;

[0094] The spray absorption tower 4 is provided with a hydrogen discharge pipe 36, a reflux condenser 8, a spray device, a packing device 15, a distributor, and a heat exchanger 34 from top to bottom; the packing device 15 of the spray absorption tower 4 is provided with tower packings; an absorbent feed pipe 24 is provided at the upper distributor of the spray absorption tower for feeding the absorbent; a crude hydrogen feed pipe 23 is provided at the lower distributor of the spray absorption tower 4 for feeding crude hydrogen; a crude absorbent discharge pipe 29 is provided at the bottom of the spray absorption tower 4;

[0095] The analytical column 5 is provided with a rectifying section 16, a distributor, a stripping section 17 and a heater 35 from top to bottom; a crude absorbent feed pipe 25 is provided on the distributor of the analytical column 5 for feeding the crude absorbent; a second reflux device is provided at the top of the analytical column 5; the reflux device includes a methanol condenser 9; the methanol condenser 9 is communicated with the reflux port 19 of the analytical column through a methanol reflux pipe; the methanol condenser 9 is provided with a recovered methanol discharge pipe 37 for discharging the recovered methanol; an absorbent discharge pipe 30 is provided at the bottom of the analytical column 5; and the absorbent discharge pipe 30 is connected to the upper distributor of the spray absorption tower 4 through the absorbent feed pipe 24 of the spray absorption tower 4.

[0096] The device of the present utility model uses methanol as a raw material. First, after mixing a part of the methanol-hydrogen mixture gas, it enters the dehydrogenation reactor through a heat exchanger and a heater. Under the catalysis of the dehydrogenation catalyst in the tubular catalyst loading tube of the catalyst packing section at a certain temperature, part of the methanol undergoes a dehydrogenation reaction to generate formaldehyde and hydrogen, forming a methanol dehydrogenation synthesis gas containing methanol, formaldehyde and hydrogen. The synthesis gas is discharged from the synthesis gas outlet at the top of the dehydrogenation reactor, and enters the distributor of the liquefaction tower through the heat exchanger and the methanol dehydrogenation synthesis gas gas-phase feed pipe. Under the action of the stripping section, rectifying section, heater and the first reflux device of the liquefaction tower, formaldehyde dissolves into a small amount of methanol to form an anhydrous formaldehyde solution, which is discharged from the anhydrous formaldehyde solution discharge pipe at the bottom of the liquefaction tower and used for the catalytic synthesis of DMMn; a high-temperature methanol and hydrogen mixture gas phase is discharged from the top of the liquefaction tower. Part of it returns to participate in the feeding, and the other part is condensed by a condenser. Most of the gaseous methanol is condensed into liquid methanol. The mixture of liquid methanol and hydrogen enters the gas-liquid separation tower together. Under the action of the reflux condenser, packing device, distributor, stripping section and heater of the liquid separation tower, pure methanol is obtained at the bottom of the tower and returned for raw material reuse. The top of the tower is hydrogen containing a small amount of methanol. The hydrogen containing a small amount of methanol enters the lower distributor of the spray absorption tower. After being countercurrently absorbed by the absorbent, relatively pure hydrogen is discharged from the hydrogen discharge pipe at the top of the tower and further processed and utilized; the absorbent (crude absorbent) that has absorbed methanol is discharged from the crude absorbent discharge pipe at the bottom of the spray absorption tower, enters the distributor of the analytical column through the crude absorbent feed pipe. Under the action of the rectifying section, distributor, stripping section and heater of the analytical column, the methanol in the absorbent is heated and vaporized, discharged from the top of the analytical column, and the recovered methanol after condensation is returned for reuse. The absorbent without methanol is discharged from the bottom of the analytical column and returned to the upper distributor of the spray absorption tower through the absorbent discharge pipe to continue to participate in methanol absorption;

[0097] The device for preparing anhydrous formaldehyde solution provided by the utility model has the characteristics of reasonable structure, smooth process, low operating pressure, convenience and flexibility, high formaldehyde selectivity, easy separation of anhydrous formaldehyde solution, convenient recycling of methanol, high atom utilization rate, safety and environmental protection, low energy consumption, etc.; it solves the problem of the source of anhydrous formaldehyde in the existing polyoxymethylene dimethyl ether synthesis technology. The investment cost of the utility model is relatively low, and the production start-up risk is relatively low. Example 1

[0098] A device for preparing anhydrous formaldehyde solution, as Figure 1 shown, includes a dehydrogenation reactor 1; a liquefaction tower 2; a gas-liquid separation tower 3; a spray absorption tower 4; an analytical tower 5; a condenser 6; a reflux condenser 7; a reflux condenser 8; a methanol condenser 9; a catalyst packing section 10; a rectifying section 11 of the liquefaction tower; a stripping section 12 of the liquefaction tower; a packing device 13 of the gas-liquid separation tower; a stripping section 14 of the gas-liquid separation tower; a packing device 15 of the spray absorption tower; a rectifying section 16 of the analytical tower; a stripping section 17 of the analytical tower; a reflux port 18 of the liquefaction tower; a reflux port 19 of the analytical tower; a gaseous methanol inlet 20 of the dehydrogenation reactor; a methanol dehydrogenation synthesis gas gas-phase feed pipe 21; a low-temperature methanol and hydrogen mixture feed pipe 22; a crude hydrogen feed pipe 23; an absorbent feed pipe 24; a crude absorbent feed pipe 25; a synthesis gas outlet 26 of the dehydrogenation reactor; an anhydrous formaldehyde solution discharge pipe 27; a methanol discharge pipe 28; a crude absorbent discharge pipe 29; an absorbent discharge pipe 30; a heater 31; a liquefaction tower heater 32; a gas-liquid separation tower heater 33; a spray absorption tower heat exchanger 34; an analytical tower heater 35; a hydrogen discharge pipe 36; a recycled methanol discharge pipe 37; a heat exchanger 38; a circulation fan 39.

[0099] Example 2

[0100] The method for preparing anhydrous formaldehyde solution by using the device of Example 1 includes the following steps:

[0101] Methanol (99%) enters the heat exchanger and heater at a rate of 21.8 kg / h, is vaporized and then enters the dehydrogenation reactor. At a certain temperature, under the catalysis of the dehydrogenation catalyst in the tube-sheet type catalyst loading tubes in the catalyst packing section, approximately 30% of the methanol undergoes a dehydrogenation reaction to produce formaldehyde and hydrogen, forming syngas with the remaining methanol. The syngas is discharged from the syngas outlet at the top of the dehydrogenation reactor and enters the distributor of the liquefaction tower through the methanol dehydrogenation syngas gas-phase feed pipe. Under the action of the stripping section, rectifying section, heater and first reflux device of the liquefaction tower, formaldehyde dissolves in a small amount of methanol to form an anhydrous formaldehyde solution (75.0% formaldehyde), which is discharged from the anhydrous formaldehyde solution discharge pipe at the bottom of the liquefaction tower at a rate of 8.2 kg / h and is used for the catalytic synthesis of DMMn; a high-temperature methanol and hydrogen mixture gas phase is discharged from the top of the liquefaction tower. A part of it returns to the heat exchanger to participate in the feed through the gas-phase transfer pipe and the recycle fan; the rest is condensed by the condenser, and most of the gaseous methanol is condensed into liquid methanol. The mixture of liquid methanol and hydrogen enters the gas-liquid separation tower together. Under the action of the reflux condenser, packing device, distributor, stripping section and heater in the gas-liquid separation tower, pure methanol of 11.63 kg / h is obtained at the bottom of the tower and returned to the raw material for reuse. The top of the tower is hydrogen containing a small amount of methanol. The hydrogen containing a small amount of methanol enters the lower distributor of the spray absorption tower. After countercurrent absorption by the absorbent, relatively pure hydrogen is discharged from the hydrogen discharge pipe at the top of the tower and is further processed and utilized; the absorbent (crude absorbent) that has absorbed methanol is discharged from the crude absorbent discharge pipe at the bottom of the spray absorption tower and enters the distributor of the stripping tower through the crude absorbent feed pipe. Under the action of the rectifying section, distributor, stripping section and heater in the stripping tower, the methanol in the absorbent is heated and vaporized and discharged from the top of the stripping tower. The recovered methanol of 1.35 kg / h after condensation is returned for reuse. The absorbent without methanol is discharged from the bottom of the stripping tower at 20 kg / h and returns to the upper distributor of the spray absorption tower through the absorbent discharge pipe to continue to participate in the methanol absorption;

[0102] After the above process is continuously fed for 10 hours, 218 kg of 99% methanol is consumed, 82 kg of 74.3% anhydrous formaldehyde solution is obtained, and a total of 129.8 kg of 99% methanol is recovered in the gas-liquid separator tower and the stripping tower; after calculation, the total formaldehyde yield is 96.8%.

[0103] In summary, a device for preparing anhydrous formaldehyde solution provided by the present utility model has the characteristics of reasonable structure, smooth process, low operating pressure, convenient and flexible operation, high formaldehyde selectivity, easy separation of anhydrous formaldehyde solution, convenient recycling of methanol, high atom utilization rate, safety and environmental protection, low energy consumption, etc.; it solves the problem of the source of anhydrous formaldehyde in the existing polyoxymethylene dimethyl ether synthesis technology. The investment cost of the present utility model is relatively low, and the production start-up risk is relatively low.

[0104] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. For example: changing the gas-liquid separation tower into an ordinary gas-liquid separator or a hydrocyclone separator; changing the spray absorption tower and the stripping tower into a cryogenic device; adding a heat recovery and utilization device to the system pipeline; adding a certain amount of nitrogen along with the methanol feed, etc. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A device for preparing anhydrous formaldehyde solution, characterized in that: According to the feeding order, it includes a dehydrogenation reactor, a liquefaction tower, a gas-liquid separation tower, a spray absorption tower, and a desorption tower connected in sequence; The dehydrogenation reactor is provided with a synthesis gas outlet, a catalyst packing section, and a gaseous methanol inlet from top to bottom; The catalyst packing section of the dehydrogenation reactor is provided with a tubular catalyst packing tube; A heater is provided in front of the inlet of the dehydrogenation reactor; A heat exchanger is provided in front of the inlet of the heater; The synthesis gas outlet of the dehydrogenation reactor is connected to the methanol dehydrogenation synthesis gas gas phase feed pipe of the liquefaction tower through a heat exchanger; The liquefaction tower is provided with a rectifying section, a distributor, a stripping section and a heater from top to bottom; A methanol dehydrogenation synthesis gas gas phase feed pipe is provided at the distributor of the liquefaction tower for feeding the methanol dehydrogenation synthesis gas gas phase; A first reflux device is provided on the top of the liquefaction tower; The first reflux device includes a high-temperature methanol and hydrogen mixture condenser, an overflow tank, a low-temperature methanol and hydrogen mixture outlet pipe and a methanol reflux pipe; The bottom of the overflow tank is connected to the reflux port of the liquefaction tower through a methanol reflux pipe; The low-temperature methanol and hydrogen mixture outlet pipe is used to discharge the low-temperature methanol and hydrogen mixture to the gas-liquid separation tower; A gas phase circulation device is provided on the top of the liquefaction tower; The gas phase circulation device comprises a gas phase conveying pipe and a circulation fan; The bottom of the liquefaction tower is provided with an anhydrous formaldehyde solution discharge pipe; The gas-liquid separation tower is provided with a reflux condenser, a packing device, a distributor, a stripping section and a heater from top to bottom; The packing device of the gas-liquid separation tower is provided with tower packing; A low-temperature methanol and hydrogen mixture feed pipe is provided at the distributor of the gas-liquid separation tower for feeding the low-temperature methanol and hydrogen mixture; A methanol discharge pipe is provided at the bottom of the gas-liquid separation tower; The spray absorption tower is provided with a hydrogen discharge pipe, a reflux condenser, a spray device, a filler device, a distributor and a heat exchanger from top to bottom; The packing device of the spray absorption tower is provided with tower packing; An absorbent feeding pipe is provided at the upper distributor of the spray absorption tower for feeding the absorbent; A crude hydrogen feed pipe is provided at the lower distributor of the spray absorption tower for feeding crude hydrogen; A crude absorbent discharge pipe is provided at the bottom of the spray absorption tower; The analytical tower is provided with a rectification section, a distributor, a stripping section and a heater from top to bottom; The distributor of the analytical tower is provided with a crude product absorbent feeding pipe for feeding the crude product absorbent; A second reflux device is provided on the top of the analytical tower; The second reflux device comprises a methanol condenser; The methanol condenser is connected to the reflux port of the analytical tower through a methanol reflux pipe; The methanol condenser is also provided with a methanol discharge pipe for extracting and recovering methanol; An absorbent discharge pipe is provided at the bottom of the analytical tower; The absorbent discharge pipe is connected to the upper distributor of the spray absorption tower.

2. The device according to claim 1, characterized in that The tubular catalyst filling tubes of the catalyst filling section of the dehydrogenation reactor are used to fill the dehydrogenation catalyst.

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