A device and method for producing high-concentration formaldehyde using methanol

Abstract

The invention discloses a device and method for producing high-concentration formaldehyde using methanol, comprising a blower, a heat exchanger, a fixed bed reactor, an absorption tower, a refining tower, and a pyrolysis tower connected in sequence; air is pressurized by the blower and mixed with a methanol raw material, flows through a heat exchanger, and then enters a fixed bed reactor for oxidation reaction; the primary product flows through a heat exchanger and then enters an absorption tower for hemiacetal reaction; the secondary reaction product flows through a refining tower and a pyrolysis tower in sequence for separation and pyrolysis; after pyrolysis, the absorbent is discharged from the bottom of the tower for recycling, and the gaseous formaldehyde product is obtained from the top of the tower for collection. The product of the invention is dry gaseous formaldehyde, which is quite stable, so the invention has obvious economic benefits and environmental advantages; the product of the invention has excellent quality: the concentration of formaldehyde is ≥99.9%, and the water is ≤0.05%.

Description

Technical Field

[0001] The present invention relates to a device and method for producing formaldehyde, in particular to a device and method for producing formaldehyde by using methanol, and further to a device and method for producing high-concentration formaldehyde by using methanol. Background Art

[0002] Formaldehyde is a very important organic chemical raw material with a wide range of uses. It is used in synthetic resins, surfactants, plastics, rubber, leather, papermaking, dyes, pharmaceuticals, pesticides, photographic films, explosives, building materials, as well as in disinfection, fumigation and preservation processes. Its main downstream products are formaldehyde polymer series, trialdehyde glue series, polyol series, heterocyclic compound series, etc., which are widely used in many industries and fields of chemical and pharmaceutical production.

[0003] Formaldehyde is a popular chemical product with a wide range of uses, simple production process and sufficient raw material supply. It is the backbone of the methanol downstream product tree. The annual global production is about 25 million tons, and about 30% of methanol is used to produce formaldehyde. However, formaldehyde products are usually a low-concentration aqueous solution, which is not convenient for long-distance transportation from an economic perspective. Therefore, factories are generally set up near major consumer markets, and import and export trade is also very rare.

[0004] The boiling point of formaldehyde is -19.5℃. It is gaseous at room temperature and usually appears in the form of aqueous solution. The concentration of the aqueous solution can reach up to 55%, generally 35% to 40%, and usually 37%. It is called formaldehyde water, commonly known as formalin. It tends to become turbid when stored for a long time in a relatively cold environment, and forms trioxymethylene precipitation at low temperatures. Formaldehyde itself can undergo condensation reactions. In general commodities, 10%-12% methanol is added as an inhibitor. Before formaldehyde is used in downstream products, impurities such as water and methanol in the formaldehyde aqueous solution must be removed first, which increases energy consumption, reduces economic benefits and puts pressure on the environment. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a device and method for producing high-concentration formaldehyde using methanol in view of the deficiencies in the prior art. The device and method use industrial methanol (GB 338-2011) qualified products or higher-quality methanol and air as raw materials, and are a technology for producing high-concentration formaldehyde using methanol.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention first provides a device for producing high-concentration formaldehyde using methanol, comprising a blower, a heat exchanger, a fixed bed reactor, an absorption tower, a refining tower, and a pyrolysis tower connected in sequence, characterized in that:

[0008] The fan is provided with a feed port I and a discharge port I, wherein: the feed port I is divided into two paths, the first path is connected to a device capable of providing air, and the second path is connected to an absorption tower; the discharge port I is connected to a heat exchanger;

[0009] The heat exchanger is provided with a cold material feed port II, a hot material discharge port II, a hot material feed port III, and a cold material discharge port III, wherein: the cold material feed port II is divided into two paths, the first path is connected to the discharge port I of the fan, and the second path is connected to the methanol storage tank; the hot material discharge port II is connected to the fixed bed reactor; the hot material feed port III is connected to the fixed bed reactor; the cold material discharge port III is connected to the absorption tower;

[0010] The fixed bed reactor is provided with a feed port IV at the top and a discharge port IV at the bottom, wherein: the feed port IV is connected to the hot material discharge port II of the heat exchanger; the discharge port IV is connected to the hot material feed port III of the heat exchanger;

[0011] The absorption tower is provided with an exhaust port I at the top and a discharge port V at the bottom, a feed port V is provided in the middle of one side of the tower wall, and a feed port VI is provided in the upper part of the other side of the tower wall, wherein: the feed port V is connected to the cold material discharge port III of the heat exchanger; the feed port VI is divided into two paths, the first path is connected to the absorbent storage tank, and the second path is connected to the pyrolysis tower; the exhaust port I is divided into two paths, the first path is connected to the feed port I of the fan, and the second path is connected to the tail gas treatment device; the discharge port V is connected to the refining tower;

[0012] The refining tower is provided with an exhaust port II at the top and a discharge port VI at the bottom, a feed port VII is provided in the middle of one side of the tower wall, and a reflux port is provided in the upper part of the other side of the tower wall, wherein: the feed port VII is connected to the discharge port V of the absorption tower; the exhaust port II is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is divided into two paths, the first path is connected to the reflux port, and the second path is connected to the methanol storage tank so as to recycle the methanol; the discharge port VI is connected to the pyrolysis tower;

[0013] The pyrolysis tower is provided with an exhaust port III at the top, a discharge port VII at the bottom, and a feed port VIII in the middle of one side of the tower wall, wherein: the feed port VIII is connected to the discharge port VI of the refining tower; the exhaust port III is connected to the product buffer tank; the discharge port VII is connected to the feed port VI of the absorption tower so that the absorbent can be recycled.

[0014] In the above technical solution, the fixed bed reactor is filled with catalyst A; the catalyst A is iron-molybdenum oxide.

[0015] In the above technical solution, the absorption tower is filled with catalyst B; the catalyst B is a solid acid catalyst, preferably a macroporous sulfonic acid cationic resin catalyst.

[0016] In the above technical solution, the catalyst B is packed in the form of a combined regular packing, and the structure of the combined regular packing is preferably the combined regular packing structure of the packed catalyst recorded in patent CN204656548U (201520253109.6).

[0017] In the above technical solution, the fan, heat exchanger, fixed bed reactor, absorption tower, refining tower and pyrolysis tower are all existing equipment in the prior art or commercially available equipment.

[0018] The present invention first provides a method for producing high-concentration formaldehyde using methanol, comprising the following steps:

[0019] (1) Oxidation reaction: air is pressurized by a blower and mixed with the methanol raw material, and then flows through the cold material feed port II, the hot material discharge port II, and the feed port IV in sequence, and then is introduced into the fixed bed reactor. The air and methanol undergo an oxidation reaction under the catalytic action of the catalyst A in the fixed bed reactor to obtain a primary reaction product, which is formaldehyde, a trace amount of formic acid and water, unreacted methanol and air; the primary reaction product flows through the discharge port IV, the hot material feed port III, the cold material discharge port III, and the feed port V in sequence, and then enters the absorption tower after heat exchange in the heat exchanger;

[0020] (2) Hemiacetal reaction: The primary reaction product formed in the fixed bed reactor enters the absorption tower, and the absorbent also enters the absorption tower from the feed port VI. The primary product and the absorbent undergo a hemiacetal reaction under the catalytic action of the catalyst B in the tower and are separated. After separation, a light component is obtained at the top of the tower. The light component is unreacted air and a trace amount of methanol, formaldehyde and absorbent. After the light component is discharged from the exhaust port I, a part of it is returned to the fan from the feed port I for recycling, and the other part is connected to the tail gas treatment device. After separation, a secondary reaction product is obtained at the bottom of the tower. The secondary reaction product is a mixture of hemiacetal obtained by the reaction of formaldehyde and absorbent, the remaining absorbent, a small amount of methanol, formic acid and a trace amount of water, which flows through the discharge port V and the feed port VII in sequence and enters the refining tower.

[0021] (3) Refining: The secondary reaction product at the bottom of the absorption tower enters the refining tower, where it is separated, and a light component is obtained at the top of the tower. The light component is gaseous methanol, formic acid, water and a trace amount of heavy components. After being discharged from the exhaust port II, it is condensed into liquid by a condenser and enters the reflux tank. A part of the material in the reflux tank is returned to the refining tower through the reflux port for recycling, and the other part is returned to the methanol storage tank for recycling. The heavy components obtained after separation are hemiacetal obtained by the reaction of methanol and absorbent and the absorbent remaining in the reaction, which flow through the discharge port VI and the feed port VIII in sequence and enter the pyrolysis tower;

[0022] (4) Pyrolysis: The heavy components at the bottom of the refining tower enter the pyrolysis tower and are pyrolyzed in the pyrolysis tower to obtain light components at the top of the tower. The light components are gaseous formaldehyde, which are discharged from the exhaust port III and connected to the formaldehyde product buffer tank. The material discharged from the outlet port VII at the bottom of the tower is the absorbent, which is returned to the absorbent storage tank for recycling.

[0023] In the above technical scheme, in step (1), as the oxidation reaction proceeds, the primary product is obtained, the temperature of the primary product is relatively high, equivalent to the hot material, and the temperature of the air and methanol is relatively low, equivalent to the cold material; the air and methanol flow through the cold material feed port II and the hot material discharge port II of the heat exchanger in sequence, and the primary product flows through the hot material feed port III and the cold material discharge port III of the heat exchanger in sequence, and the cold and hot materials are heat exchanged in the heat exchanger; after the methanol is heated to vaporized methanol after heat exchange, it enters the fixed bed reactor together with the air to react, and the primary product is cooled after heat exchange and then enters the absorption tower.

[0024] In the above technical solution, in step (1), the methanol raw material is a qualified product or higher grade methanol that meets the requirements of industrial methanol GB 338-2011.

[0025] In the above technical solution, in step (1), the air is pressurized by a fan to 0.20-0.40 MPa.

[0026] In the above technical solution, in step (1), the volume ratio of methanol to air after vaporization is 3 to 8:100, preferably 5.5 to 6.5:100.

[0027] In the above technical scheme, in step (1), the volume space velocity of methanol after vaporization and air into the fixed bed reactor is 2 to 10 h -1 .

[0028] In the above technical solution, in step (1), the reaction temperature in the fixed bed reactor is 300-360°C, preferably 345-355°C, and the reaction pressure is 0.15-0.25Mpa.

[0029] In the above technical solution, in step (1), the catalyst A is an iron-molybdenum oxide, including iron molybdate and molybdenum trioxide, and the molar ratio of molybdenum to iron is 1.8 to 3.3:1.

[0030] In the above technical solution, in step (2), the primary reaction product formed in the fixed bed reactor enters the absorption tower at a volume space velocity of 1 to 6 h -1 .

[0031] In the above technical solution, in step (2), the catalyst B is a solid acid catalyst, preferably a macroporous sulfonic acid cationic resin catalyst.

[0032] In the above technical solution, in step (2), the hemiacetal reaction has the following reaction conditions: reaction temperature is 70-100° C., and reaction pressure is 0.10-0.20 MPa.

[0033] In the above technical scheme, in step (2), the operating conditions of the absorption tower are: the top temperature is 70-100°C and the pressure is 0.10-0.15Mpa; the bottom temperature is 70-100°C and the pressure is 0.10-0.25Mpa.

[0034] In the above technical scheme, in step (2), during the absorption process in the absorption tower, an excess of absorbent is introduced from the feed port VI, which is conducive to the reaction in the direction of absorbing formaldehyde; the molar ratio of the absorbent to methanol is 1 to 2:1, preferably 1.1-1.3:1.

[0035] In the above technical solution, in step (2), the absorbent is any one of alcohols such as n-heptanol, benzyl alcohol, cyclohexyl methanol, etc. with a boiling point of 160-210°C, or a mixture of two or more alcohols in any proportion.

[0036] In the above technical scheme, in step (3), the refining tower has the following operating conditions: the tower top temperature is 75-105°C, the pressure is 0.05-0.10Mpa, the tower bottom temperature is 95-115°C, and the pressure is 0.10-0.15Mpa.

[0037] In the above technical solution, in step (4), the operating conditions of the pyrolysis tower are: the top temperature is 140-150°C and the pressure is 0.10-0.15Mpa, and the bottom temperature is 140-150°C and the pressure is 0.10-0.25Mpa.

[0038] The advantages of the technical solution of the present invention are:

[0039] (1) The product of the present invention has excellent quality: the concentration of formaldehyde is ≥99.9%, and the concentration of water is ≤0.05%.

[0040] (2) The special property of formaldehyde is that it is easy to polymerize. It usually appears in the form of an aqueous solution containing 10%-12% methanol as an inhibitor. Pure formaldehyde must be prepared before it is used in downstream products, generating a large amount of wastewater and by-product methanol, which greatly increases energy consumption. The product of the present invention is dry gaseous formaldehyde, which is quite stable. Therefore, the present invention has obvious economic benefits and environmental advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : Schematic diagram of the overall structure of the device of the present invention;

[0042] Figure 2 : Process flow chart of the method of the present invention;

[0043] Among them: 1 is a fan, 2 is a heat exchanger, 3 is a fixed bed reactor, 4 is an absorption tower, 5 is a refining tower, and 6 is a pyrolysis tower. DETAILED DESCRIPTION

[0044] The specific implementation of the technical solution of the present invention is described in detail below, but the present invention is not limited to the following description:

[0045] The present invention first provides a device for producing high-concentration formaldehyde using methanol, comprising a blower 1, a heat exchanger 2, a fixed bed reactor 3, an absorption tower 4, a refining tower 5, and a pyrolysis tower 6 connected in sequence. Figure 1 As shown:

[0046] The fan 1 is provided with a feed port I and a discharge port I, wherein: the feed port I is divided into two paths, the first path is connected to a device capable of providing air, and the second path is connected to an absorption tower 4; the discharge port I is connected to a heat exchanger 2;

[0047] The heat exchanger 2 is provided with a cold material feed port II, a hot material discharge port II, a hot material feed port III, and a cold material discharge port III, wherein: the cold material feed port II is divided into two paths, the first path is connected to the discharge port I of the fan 1, and the second path is connected to the methanol storage tank; the hot material discharge port II is connected to the fixed bed reactor 3; the hot material feed port III is connected to the fixed bed reactor 3; the cold material discharge port III is connected to the absorption tower 4;

[0048] The fixed bed reactor 3 is provided with a feed port IV at the top and a discharge port IV at the bottom, wherein: the feed port IV is connected to the hot material discharge port II of the heat exchanger 2; the discharge port IV is connected to the hot material feed port III of the heat exchanger 2;

[0049] The absorption tower 4 is provided with an exhaust port I at the top and a discharge port V at the bottom, a feed port V is provided in the middle of one side of the tower wall, and a feed port VI is provided in the upper part of the other side of the tower wall, wherein: the feed port V is connected to the cold material discharge port III of the heat exchanger 2; the feed port VI is divided into two paths, the first path is connected to the absorbent storage tank, and the second path is connected to the pyrolysis tower 6; the exhaust port I is divided into two paths, the first path is connected to the feed port I of the fan 1, and the second path is connected to the tail gas treatment device; the discharge port V is connected to the refining tower 5;

[0050] The refining tower 5 is provided with an exhaust port II at the top and a discharge port VI at the bottom, a feed port VII is provided in the middle of one side of the tower wall, and a reflux port is provided in the upper part of the other side of the tower wall, wherein: the feed port VII is connected to the discharge port V of the absorption tower 4; the exhaust port II is connected to the condenser and the reflux tank in sequence, the outlet of the reflux tank is divided into two paths, the first path is connected to the reflux port, and the second path is connected to the methanol storage tank so as to recycle the methanol; the discharge port VI is connected to the pyrolysis tower 6;

[0051] The pyrolysis tower 6 is provided with an exhaust port III at the top, a discharge port VII at the bottom, and a feed port VIII in the middle of one side of the tower wall, wherein: the feed port VIII is connected to the discharge port VI of the refining tower 5; the exhaust port III is connected to the product buffer tank; the discharge port VII is connected to the feed port VI of the absorption tower 4 so that the absorbent can be recycled.

[0052] In the present invention, the fixed bed reactor 3 is filled with catalyst A; the catalyst A is iron-molybdenum oxide.

[0053] In the present invention, the absorption tower 4 is filled with a catalyst B; the catalyst B is a solid acid catalyst, preferably a macroporous sulfonic acid cationic resin catalyst.

[0054] In the present invention, the catalyst B is packed in the form of a combined regular packing, and the structure of the combined regular packing is preferably the combined regular packing structure of the packed catalyst recorded in patent CN204656548U (201520253109.6).

[0055] In the present invention, the fan, heat exchanger, fixed bed reactor, absorption tower, refining tower and pyrolysis tower are all existing equipment in the prior art or commercially available equipment.

[0056] The present invention first provides a method for producing high-concentration formaldehyde using methanol, the flow chart is as follows: Figure 2 As shown, the following steps are included:

[0057] (1) Oxidation reaction: air is pressurized by a blower 1 and mixed with the methanol raw material, and then flows through the cold material feed port II, the hot material discharge port II, and the feed port IV in sequence, and then enters the fixed bed reactor 3. The air and methanol undergo an oxidation reaction under the catalytic action of the catalyst A in the fixed bed reactor 3 to obtain a primary reaction product, which is formaldehyde, a trace amount of formic acid and water, unreacted methanol, and air. The primary reaction product flows through the discharge port IV, the hot material feed port III, the cold material discharge port III, and the feed port V in sequence, and then enters the absorption tower 4 after heat exchange in the heat exchanger 2;

[0058] (2) Hemiacetal reaction: The primary reaction product formed in the fixed bed reactor 3 enters the absorption tower 4, and the absorbent also enters the absorption tower from the feed port VI. The primary product and the absorbent undergo a hemiacetal reaction under the catalytic action of the catalyst B in the tower and are separated. After separation, a light component is obtained at the top of the tower. The light component is unreacted air and a trace amount of methanol, formaldehyde and absorbent. After the light component is discharged from the exhaust port I, a part of it is returned to the fan 1 from the feed port I for recycling, and the other part is connected to the tail gas treatment device. After separation, the secondary reaction product is obtained at the bottom of the tower. The secondary reaction product is a mixture of hemiacetal obtained by the reaction of formaldehyde and the absorbent, the remaining absorbent, a small amount of methanol, formic acid, and a trace amount of water. It flows through the discharge port V and the feed port VII in sequence and enters the refining tower 5;

[0059] (3) Refining: The secondary reaction product at the bottom of the absorption tower (4) enters the refining tower 5, where it is separated and a light component is obtained at the top of the tower. The light component is gaseous methanol, formic acid, water and a trace amount of heavy components. After being discharged from the exhaust port II, it is condensed into liquid by a condenser and enters the reflux tank. A part of the material in the reflux tank is returned to the refining tower 5 through the reflux port for recycling, and the other part is returned to the methanol storage tank for recycling. The heavy components obtained after separation are hemiacetal obtained by the reaction of methanol and absorbent and the absorbent remaining in the reaction, which flow through the discharge port VI and the feed port VIII in sequence and enter the pyrolysis tower 6;

[0060] (4) Pyrolysis: The heavy components at the bottom of the refining tower 5 enter the pyrolysis tower 6, where they are pyrolyzed to obtain light components at the top of the tower. The light components are gaseous formaldehyde, which are discharged from the exhaust port III and connected to the formaldehyde product buffer tank. The material discharged from the outlet port VII at the bottom of the tower is the absorbent, which is returned to the absorbent storage tank for recycling.

[0061] The present invention will be described below in conjunction with specific embodiments:

[0062] Embodiment 1:

[0063] A method for producing high-concentration formaldehyde using methanol, specifically comprising the following steps:

[0064] (1) Oxidation reaction: After the air is pressurized by fan 1, it is mixed with industrial methanol (GB 338-2011) as raw material. The methanol is vaporized and mixed with air in a volume ratio of 6:100. After that, it flows through heat exchanger 2 and is discharged from feed port IV (volume space velocity is 5h -1 ) is introduced into the fixed bed reactor 3, and the air and methanol are oxidized under the catalytic action of the catalyst A (including iron molybdate and molybdenum trioxide, with a molar ratio of molybdenum to iron of 3:1) in the fixed bed reactor 3, the reaction temperature is 345-350°C, the reaction pressure is 0.18-0.20Mpa, and the primary reaction product is obtained; the primary reaction product is a mixture of formaldehyde, unreacted methanol, formic acid, and water. The primary reaction product flows through the discharge port IV and the feed port III in sequence, enters the heat exchanger 2 for heat exchange, and then enters the absorption tower 4;

[0065] (2) Hemiacetal reaction: The primary reaction product formed in the fixed bed reactor 3 enters the absorption tower 4 (the volume space velocity is 4h -1 ), and the absorbent benzyl alcohol reacts with the catalyst B (catalyst B is KC107 catalyst of Kairui Environmental Protection Technology Co., Ltd.) in the tower for hemiacetal reaction, and is separated; the molar ratio of benzyl alcohol to methanol is 1.2:1. After separation, the light component is obtained at the top of the tower, which is unreacted air, trace methanol, formaldehyde and absorbent, etc. After being discharged from the exhaust port I, a part of it is returned to the fan 1 from the feed port I for recycling, and the other part is connected to the tail gas treatment device; after separation, the secondary reaction product is obtained at the bottom of the tower, which is a mixture of hemiacetal obtained by the reaction of formaldehyde and benzyl alcohol, the absorbent remaining in the reaction, a small amount of methanol, trace water and formic acid, which flows through the discharge port V and the feed port VII in sequence and enters the refining tower 5; the operating conditions of the absorption tower 4 are: the top temperature is 80°C, the pressure is 0.12Mpa, the bottom temperature is 85°C, and the pressure is 0.14Mpa.

[0066] In this embodiment, the catalyst loading form refers to the combined structured packing of the catalyst loaded in patent CN204656548U (201520253109.6), including: a plurality of catalyst mold pieces filled with catalyst particles, a plurality of metal perforated plate corrugated packing pieces 2 and a bundled steel belt; the catalyst mold piece is formed by pressing a metal diamond plate lined with a metal wire mesh of the same material into a prescribed shape, and then loading the catalyst particles and spot welding and sealing; the catalyst particles can have a variety of shapes. The catalyst particles given in this embodiment are spherical particles with a diameter of 0.355-1.25 mm; the catalyst mold piece A 4×8 stainless steel diamond plate mesh and a 60-mesh stainless steel wire mesh of the same material are spot-welded and composited, and then pressed into two isosceles trapezoidal structures with a cross-section bottom angle of not less than 60°, and both ends are sealed; the metal orifice plate filler sheet is 150-700X type or 150-700Y type, and the present embodiment uses a 700Y type stainless steel orifice plate corrugated filler sheet; a plurality of catalyst mold sheets and stainless steel orifice plate corrugated filler sheets 2 are linearly and evenly spaced and staggered along the tower diameter direction, and then tied with a steel belt of the same material, and finally an anti-wall flow ring is installed to further ensure the stability of the catalytic distillation element and the catalytic distillation effect, and at the same time, it is more convenient when installing into the tower.

[0067] (3) Refining: The secondary reaction product at the bottom of the absorption tower enters the refining tower 5, where it is separated. The operating conditions are: the tower top temperature is 95°C and the pressure is 0.06Mpa, and the tower bottom temperature is 105°C and the pressure is 0.11Mpa. The light components are obtained at the top of the tower. The light components are gaseous methanol, formic acid, water and trace heavy components. After being discharged from the exhaust port II, they are condensed into liquid by the condenser and enter the reflux tank. Part of the material in the reflux tank is returned to the refining tower 5 through the reflux port for recycling, and the other part is returned to the methanol storage tank for recycling. The heavy substances discharged from the tower bottom outlet VI are hemiacetal generated by the reaction of methanol and benzyl alcohol and the remaining absorbent.

[0068] (4) Pyrolysis: The hemiacetal at the bottom of the refining tower 5 enters the pyrolysis tower 6, where it is pyrolyzed to obtain a light component at the top of the tower. The light component is gaseous formaldehyde and is connected to the formaldehyde product buffer tank. The material discharged from the bottom outlet VII of the tower is the absorbent, which is returned to the absorbent storage tank for recycling. The operating conditions of the pyrolysis tower are: the top temperature is 145°C and the pressure is 0.12 MPa, and the bottom temperature is 145°C and the pressure is 0.12 MPa.

[0069] In the product of this embodiment, the concentration of formaldehyde is 99.92%, and the concentration of water is 0.04%.

[0070] Embodiment 2:

[0071] A method for producing high-concentration formaldehyde using methanol, specifically comprising the following steps:

[0072] (1) Oxidation reaction: After the air is pressurized by fan 1, it is mixed with qualified industrial methanol (GB 338-2011) as raw material, and the volume ratio of vaporized methanol to air is 5.5:100. After passing through heat exchanger 2, it is discharged from feed port IV (volume space velocity is 5h -1 ) is introduced into the fixed bed reactor 3, and the air and methanol are oxidized under the catalytic action of the catalyst A (same as in Example 1) in the fixed bed reactor, the reaction temperature is 345-350°C, the reaction pressure is 0.18-0.20Mpa, and the primary reaction product is obtained; the primary reaction product is a mixture of formaldehyde, unreacted methanol, formic acid, and water. The primary reaction product flows through the discharge port IV and the feed port III in sequence, enters the heat exchanger 2 for heat exchange, and then enters the absorption tower 4;

[0073] (2) Hemiacetal reaction: The primary reaction product formed in the fixed bed reactor 3 enters the absorption tower 4 (space velocity is 4h -1 ), and the absorbent n-heptanol reacts with the catalyst B (the catalyst B and the arrangement of the combined regular packing are the same as those in Example 1) in the tower to undergo a hemiacetal reaction, and is separated; the molar ratio of n-heptanol to methanol is 1.15:1. After separation, a light component is obtained at the top of the tower, which is unreacted air, a trace of methanol, formaldehyde and absorbent, etc. After being discharged from the exhaust port I, a part of it is returned to the fan 1 from the feed port I for recycling, and the other part is connected to the tail gas treatment device; after separation, a secondary reaction product is obtained at the bottom of the tower, which is a mixture of hemiacetal obtained by the reaction of formaldehyde and n-heptanol, the absorbent remaining in the reaction, a small amount of methanol, a trace of water and formic acid, which flows through the discharge port V and the feed port VII in sequence and enters the refining tower 5; the operating conditions of the absorption tower 4 are: the top temperature is 83°C, the pressure is 0.13Mpa, the bottom temperature is 87°C, and the pressure is 0.15Mpa.

[0074] (3) Refining: The secondary reaction product at the bottom of the absorption tower 4 enters the refining tower 5, where it is separated. The operating conditions are: the top temperature is 97°C and the pressure is 0.06Mpa, and the bottom temperature is 108°C and the pressure is 0.11Mpa. The light components are obtained at the top of the tower. The light components are gaseous methanol, formic acid, water and trace heavy components. After being discharged from the exhaust port II, they are condensed into liquid by the condenser and enter the reflux tank. Part of the material in the reflux tank is returned to the refining tower through the reflux port for recycling, and the other part is returned to the methanol storage tank for recycling. The heavy substances discharged from the bottom outlet VI are hemiacetal and residual absorbent generated by the reaction of methanol and n-heptanol.

[0075] (4) Pyrolysis: The hemiacetal at the bottom of the refining tower 5 enters the pyrolysis tower 6, where it is pyrolyzed to obtain a light component at the top of the tower. The light component is gaseous formaldehyde and is connected to the formaldehyde product buffer tank. The material discharged from the bottom outlet VII is mainly absorbent, which is returned to the absorbent storage tank for recycling. The operating conditions of the pyrolysis tower are: the top temperature is 147°C and the pressure is 0.13 MPa, and the bottom temperature is 147°C and the pressure is 0.13 MPa.

[0076] In the product of this embodiment, the concentration of formaldehyde is 99.94%, and the concentration of water is 0.03%.

[0077] The above examples are only for illustrating the technical concept and technical features of the present invention, and cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing high-concentration formaldehyde using methanol, characterized in that: The following steps are involved: (1) Oxidation reaction: air is pressurized by a blower (1) and mixed with methanol raw material, and then flows through a cold material feed port II, a hot material discharge port II, and a feed port IV in sequence and then enters a fixed bed reactor (3). The air and methanol undergo an oxidation reaction under the catalytic action of a catalyst A in the fixed bed reactor (3) to obtain a primary reaction product, wherein the primary product is formaldehyde, a trace amount of formic acid and water, unreacted methanol, and air. The primary reaction product flows through a discharge port IV, a hot material feed port III, a cold material discharge port III, and a feed port V in sequence, and then enters an absorption tower (4) after heat exchange through a heat exchanger (2); the catalyst A is iron molybdate and molybdenum trioxide, and the molar ratio of molybdenum to iron is 1.8 to 3.3:1; (2) Hemiacetal reaction: The primary reaction product formed in the fixed bed reactor (3) enters the absorption tower (4), and the absorbent also enters the absorption tower from the feed port VI. The primary product and the absorbent undergo a hemiacetal reaction under the catalytic action of the catalyst B in the tower and are separated. After separation, a light component is obtained at the top of the tower. The light component is unreacted air and a trace amount of methanol, formaldehyde and absorbent. After the light component is discharged from the exhaust port I, a part of it returns to the fan (1) from the feed port I for recycling, and the other part is connected to the exhaust gas treatment device. After separation, a light component is obtained at the bottom of the tower. The secondary reaction product is a mixture of hemiacetal obtained by the reaction of formaldehyde and absorbent, the absorbent remaining in the reaction, a small amount of methanol, formic acid, and a trace amount of water, which flows through the discharge port V and the feed port VII in sequence and then enters the refining tower (5); the absorbent is any one of n-heptanol, benzyl alcohol, and cyclohexyl methanol with a boiling point of 160 to 210° C., or a mixture of two or more of them in any proportion; the molar ratio of the absorbent to methanol is 1 to 2:1; the catalyst B is a macroporous sulfonic acid cationic resin catalyst; The hemiacetal reaction has the following reaction conditions: reaction temperature of 70-100°C and reaction pressure of 0.10-0.20 MPa; the absorption tower (4) has the following operating conditions: tower top temperature of 70-100°C and pressure of 0.10-0.15 MPa; tower bottom temperature of 70-100°C and pressure of 0.10-0.25 MPa; (3) Refining: The secondary reaction product at the bottom of the absorption tower (4) enters the refining tower (5), where it is separated and a light component is obtained at the top of the tower. The light component is gaseous methanol, formic acid, water and a trace amount of heavy components. After being discharged from the exhaust port II, it is condensed into liquid by a condenser and enters the reflux tank. A part of the material in the reflux tank is returned to the refining tower (5) through the reflux port for recycling, and the other part is returned to the methanol storage tank for recycling. The heavy components obtained after separation are hemiacetal obtained by the reaction of methanol and absorbent and the absorbent remaining in the reaction, which flow through the discharge port VI and the feed port VIII in sequence and enter the pyrolysis tower (6); (4) Pyrolysis: The heavy components at the bottom of the refining tower (5) enter the pyrolysis tower (6) and are pyrolyzed in the pyrolysis tower (6) to obtain light components at the top of the tower. The light components are gaseous formaldehyde, which are discharged from the exhaust port III and connected to the formaldehyde product buffer tank. The material discharged from the outlet port VII at the bottom of the tower is the absorbent, which is returned to the absorbent storage tank for recycling. The operating conditions of the pyrolysis tower (6) are: the top temperature is 140-150°C and the pressure is 0.10-0.15Mpa, and the bottom temperature is 140-150°C and the pressure is 0.10-0.25Mpa.

2. The method according to claim 1, characterized in that In step (1), as the oxidation reaction proceeds, a primary product is obtained. The temperature of the primary product is relatively high, equivalent to a hot material, while the temperature of the air and methanol is relatively low, equivalent to a cold material. The air and methanol flow through the cold material feed port II and the hot material discharge port II of the heat exchanger in sequence, and the primary product flows through the hot material feed port III and the cold material discharge port III of the heat exchanger in sequence. The hot and cold materials are heat exchanged in the heat exchanger. After the methanol is heated to vaporized methanol after the heat exchange, it enters the fixed bed reactor together with the air to react. After the primary product is cooled after the heat exchange, it enters the absorption tower (4).

3. The method according to claim 1, characterized in that: In step (1), the methanol raw material is a qualified product that meets the requirements of industrial methanol GB 338-2011 or a higher grade of methanol; the air is pressurized by a blower to 0.20-0.40 MPa.

4. The method according to claim 1 or 2, characterized in that: In step (1), the volume ratio of vaporized methanol to air is 3-8:100; the volume space velocity of vaporized methanol and air introduced into the fixed bed reactor (3) is 2-10 h -1 .

5. The method according to claim 1, characterized in that: In step (1), in the fixed bed reactor (3), the reaction temperature therein is 300-360° C., and the reaction pressure is 0.15-0.25 MPa.

6. The method according to claim 1, characterized in that In step (2), the primary reaction product formed in the fixed bed reactor (3) enters the absorption tower (4) at a volume space velocity of 1 to 6 h -1 .

7. The method according to claim 1, characterized in that In step (3), the refining tower (5) has the following operating conditions: the tower top temperature is 75-105°C, the pressure is 0.05-0.10 MPa, and the tower bottom temperature is 95-115°C, the pressure is 0.10-0.15 MPa.

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