Process and apparatus for the recovery of dilute aldehydes

Abstract

The present application provides a kind of recovery method and device of dilute aldehyde, the recovery method of dilute aldehyde includes the following steps: adding neutralizing agent to dilute aldehyde raw material liquid, the pH value of dilute aldehyde raw material liquid is 6.2-6.8, then rectification recovery treatment is carried out, obtains trioxymethylene material and heavy component material;Dehydration treatment is carried out to heavy component material, obtains dilute formaldehyde material and waste water material;It can recover the dilute aldehyde generated in trioxymethylene production, improve the recovery efficiency of trioxymethylene and formaldehyde in dilute aldehyde, reduce production cost.

Description

Technical Field

[0001] This invention belongs to the field of chemical recycling and energy-saving technology, specifically relating to a method and apparatus for recovering dilute aldehydes. Background Technology

[0002] Polyoxymethylene (POM) is one of the five most widely used engineering plastics. Trioxymethylene (C3H6O3) is an important intermediate for POM. Currently, industrially used trioxymethylene is typically synthesized from formaldehyde (CH2O) in a large-scale reaction system under the catalysis of acidic components. This process usually involves formaldehyde concentration, synthetic distillation, extractive distillation, removal of light and heavy components, etc., to obtain polymer-grade trioxymethylene, which is then used to prepare POM engineering plastics. This is because POM preparation requires high-purity polymerization raw materials. Formaldehyde, when existing as a monomer, is a gas, resulting in low polymerization efficiency and high sensitivity to impurities. Therefore, formaldehyde is generally first concentrated and prepared into relatively stable trioxymethylene, which is then dehydrated and purified to obtain high-purity trioxymethylene, which is then used as the direct raw material for POM preparation.

[0003] During the concentration and refining of formaldehyde and trioxymethylene, a dilute aldehyde solution containing formaldehyde, trioxymethylene and a small amount of impurities is generated. Direct discharge of this solution not only wastes aldehyde materials but also makes the waste liquid difficult to treat. Therefore, industrial processes typically require a dilute aldehyde recovery process to recover aldehydes from the dilute aldehyde solution and to minimize the aldehyde content in the wastewater to reduce wastewater treatment costs.

[0004] Among the existing methods for recovering dilute aldehydes, some directly prepare the downstream product pentaerythritol from dilute aldehydes, while others use a distillation scheme that combines two distillation towers. However, due to the limited technology and production levels of various enterprises, the recovery efficiency of dilute aldehydes remains low. Summary of the Invention

[0005] This invention provides a method for recovering dilute aldehydes to solve the problem of low recovery efficiency of formaldehyde and trioxymethylene in existing trioxymethylene production.

[0006] The present invention also provides a dilute aldehyde recovery device for performing the above-described recovery method to improve the recovery efficiency of formaldehyde and trioxymethylene in dilute aldehyde.

[0007] On the one hand, the present invention provides a method for recovering dilute aldehydes, comprising the following steps:

[0008] A neutralizing agent is added to the dilute aldehyde raw material solution and mixed to make the pH value of the dilute aldehyde raw material solution 6.2-6.8. Then, the solution is subjected to distillation and recovery treatment to obtain trioxymethylene material and heavy component material.

[0009] The recombinant material is dehydrated to obtain dilute formaldehyde and wastewater.

[0010] Furthermore, it also includes the following steps:

[0011] The dilute formaldehyde material is subjected to a light component removal treatment to obtain light component product material and dilute formaldehyde recycled material, which is then reused in the distillation and recovery process.

[0012] Furthermore, prior to the distillation and recovery process, the dilute aldehyde feedstock liquid undergoes a first preheating treatment; wherein at least a portion of the dilute formaldehyde material is used as a heat source medium in the first preheating treatment to obtain cooled dilute formaldehyde material, which is then subjected to the light-weight removal treatment; and / or,

[0013] At least a portion of the dilute formaldehyde material is used as a heat source medium in the distillation and recovery process; and / or,

[0014] Prior to the dehydration treatment, the material undergoes a second preheating treatment; wherein the wastewater material is used as a heat source medium in the second preheating treatment; and / or,

[0015] At least a portion of the dilute formaldehyde material is used as a heat source medium in the removal of light elements to obtain the cooled dilute formaldehyde material, which is then subjected to the removal of light elements.

[0016] Furthermore, it also includes performing waste heat recovery treatment on at least a portion of the dilute formaldehyde material to obtain the cooled dilute formaldehyde material, and then subjecting the cooled dilute formaldehyde material to the light-removal treatment.

[0017] Furthermore, prior to the removal of light components, the cooled dilute formaldehyde material is further concentrated to obtain concentrated formaldehyde material and light component material, and the light component material is then subjected to the removal of light components.

[0018] Furthermore, the top pressure of the distillation recovery treatment is 0-0.1 MPaG, the top temperature is 70-120°C, and the bottom temperature is 80-130°C; and / or,

[0019] The dehydration treatment has a top pressure of 0.6-2 MPaG, a top temperature of 160-200℃, and a bottom temperature of 170-210℃; and / or,

[0020] The concentration process is operated at a pressure of -0.095 to 0.1 MPaG; and / or,

[0021] The top pressure of the light-removal treatment is 0-0.1 MPaG, the top temperature is 50-100℃, and the bottom temperature is 60-110℃.

[0022] On the other hand, the present invention also provides a dilute aldehyde recovery device for the above-mentioned recovery method; the recovery device includes a distillation recovery unit and a dehydration unit;

[0023] The distillation recovery unit is provided with a first feed inlet, which is the inlet of the recovery device; the top outlet of the distillation recovery unit is used to output trioxymethylene material, and the bottom outlet of the distillation recovery unit is connected to the second feed inlet located in the dehydration unit.

[0024] The bottom outlet of the dehydration unit is used to discharge wastewater material, and the top outlet of the dehydration unit is used to discharge dilute formaldehyde material.

[0025] Furthermore, the recycling device also includes a light-weight removal unit;

[0026] The top outlet of the dehydration unit is also connected to the third inlet of the light component removal unit. The top outlet of the light component removal unit is used to output light component product material, and the bottom outlet of the light component removal unit is connected to the first inlet.

[0027] Furthermore, the recovery device also includes a first preheating unit, a second preheating unit, a waste heat recovery unit, a first reboiling unit, a second reboiling unit, and a third reboiling unit;

[0028] Wherein, the material inlet of the first preheating unit is the inlet of the recovery device, and the material outlet of the first preheating unit is connected to the first feed inlet; the bottom outlet of the distillation recovery unit is connected to the second feed inlet of the dehydration unit via the second preheating unit, the bottom outlet of the distillation recovery unit is connected to the material inlet of the second preheating unit, and the material outlet of the second preheating unit is connected to the second feed inlet of the dehydration unit.

[0029] The bottom outlet of the distillation recovery unit is also connected to the material inlet of the first reboiler unit, and the material outlet of the first reboiler unit is connected to the lower reflux port of the distillation recovery unit; the bottom outlet of the dehydration unit is also connected to the material inlet of the second reboiler unit, and the material outlet of the second reboiler unit is connected to the lower reflux port of the dehydration unit; the bottom outlet of the light-light removal unit is also connected to the material inlet of the third reboiler unit, and the material outlet of the third reboiler unit is connected to the lower reflux port of the light-light removal unit.

[0030] The top outlet of the dehydration unit is also connected to the heat medium inlet of the first preheating unit, the heat medium inlet of the distillation recovery unit, the heat medium inlet of the third reboiling unit, and the heat medium inlet of the waste heat recovery unit, respectively. The heat medium outlet of the first preheating unit, the heat medium outlet of the distillation recovery unit, the heat medium outlet of the third reboiling unit, and the heat medium outlet of the waste heat recovery unit are respectively connected to the third feed inlet of the light-duty removal unit.

[0031] The bottom outlet of the dewatering unit is connected to the heat medium inlet of the second preheating unit, and the heat medium outlet of the second preheating unit is used to output the wastewater material.

[0032] Furthermore, the recycling device also includes a concentration unit;

[0033] The heat medium outlets of the first preheating unit, the distillation recovery unit, the third reboiling unit, and the waste heat recovery unit are all connected to the inlet of the concentration unit. The top outlet of the concentration unit is connected to the third feed inlet of the light precipitator unit. The bottom outlet of the concentration unit is used to output concentrated formaldehyde material.

[0034] This invention provides a method for recovering dilute aldehydes, which can recover dilute aldehydes generated during the production of trioxymethylene, improve the recovery efficiency of trioxymethylene and formaldehyde in dilute aldehydes, and reduce production costs. Attached Figure Description

[0035] Figure 1 A schematic diagram of a recycling device in a specific embodiment of the present invention;

[0036] Figure 2 A schematic diagram of a recycling device in a specific embodiment of the present invention;

[0037] Figure 3 A schematic diagram of a recycling device in a specific embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of a recycling device in a specific embodiment of the present invention.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1: First preheating unit; 2: Distillation recovery unit; 3: First reboiler unit; 4: Second preheating unit; 5: Dehydration unit; 6: Second reboiler unit; 7: Waste heat recovery unit; 8: Concentration unit; 9: Light weight removal unit; 10: Third reboiler unit. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] On the one hand, the present invention provides a method for recovering dilute aldehydes, comprising the following steps:

[0043] A neutralizing agent is added to the dilute aldehyde raw material solution and mixed to make the pH value of the dilute aldehyde raw material solution 6.2-6.8. Then, the solution is subjected to distillation and recovery treatment to obtain trioxymethylene material and heavy component material.

[0044] The heavy component material is dehydrated to obtain dilute formaldehyde material and wastewater material.

[0045] The dilute aldehydes produced in the main production process of trioxymethylene mainly come from formaldehyde concentration, trioxymethylene reaction, and refining processes. Besides unreacted formaldehyde raw materials and entrained trioxymethylene products, dilute aldehydes typically contain various impurities. Direct discharge not only wastes aldehyde materials but also results in difficult-to-treat waste liquid. This invention provides a method for recovering dilute aldehydes from the trioxymethylene production process. The dilute aldehyde raw material liquid refers to a solution containing water, trioxymethylene, formaldehyde, and other impurities. Based on boiling point, the impurities in the dilute aldehyde raw material liquid are divided into two types: one is light component impurities with lower boiling points, including one or more of methanol, methyl formate, dioxane, dioxane, ethylene oxide, benzene, cyclohexane, and methylal; the other is heavy component impurities with higher boiling points, mainly consisting of acidic components and their salts, including one or more of formic acid, sodium formate, potassium formate, sulfuric acid, sodium sulfate, sodium bisulfate, potassium sulfate, and potassium bisulfate.

[0046] It is understandable that, in order to prevent acidic components such as formic acid and sulfuric acid in the dilute aldehyde raw material liquid from accumulating in the system and corroding equipment and pipelines, it is usually necessary to use a neutralizing agent to neutralize the formic acid and sulfuric acid in the dilute aldehyde, so that they react to form corresponding salts. Subsequently, the corresponding salts are separated from the system by recovery and distillation and then treated as wastewater. Optionally, the neutralizing agent includes at least one of sodium hydroxide and potassium hydroxide.

[0047] Specifically, a neutralizing agent is added to the dilute aldehyde feedstock solution and mixed to adjust the pH value of the solution to 6.2-6.8. The solution is then subjected to distillation and recovery treatment to obtain trioxymethylene and heavy component materials. The trioxymethylene material recovers most of the trioxymethylene and a small amount of formaldehyde from the dilute aldehyde feedstock solution and can be directly recycled back to the main trioxymethylene production process for further purification. The main components of the heavy component material are formaldehyde, acidic components, and their salts.

[0048] The heavy component material is dehydrated to obtain dilute formaldehyde material and wastewater material. The dilute formaldehyde material recovers most of the formaldehyde, water and a small amount of light components from the dilute formaldehyde raw material liquid. The dilute formaldehyde material can be directly recycled back to the main production process of trioxymethylene for reaction. The wastewater material discharges most of the water and acidic components and their salts from the formaldehyde raw material liquid. The acidic components and their salts are discharged with the wastewater to prevent a large amount of water and acidic components and their salts from returning to the main process of trioxymethylene and accumulating, thereby affecting the product quality of trioxymethylene and the stable operation of the equipment.

[0049] This invention provides a method for recovering dilute aldehydes. The method involves recovering most of the paraformaldehyde and a small portion of the formaldehyde from the dilute aldehyde feedstock through distillation. Further dehydration recovers most of the remaining formaldehyde from the feedstock, while also removing wastewater, acidic components, and their salts. This significantly reduces the amount of water, acidic components, and their salts that would otherwise be returned to the main paraformaldehyde process, improving the quality of the paraformaldehyde product and ensuring stable operation of the equipment. This method achieves highly efficient recovery of dilute aldehydes by recovering most of the paraformaldehyde and formaldehyde.

[0050] Optionally, the process also includes the following steps: removing light components from the dilute formaldehyde material to obtain light component product material and dilute formaldehyde recycled material, so that the dilute formaldehyde recycled material can be reused in the distillation and recovery process.

[0051] Dilute formaldehyde material containing most formaldehyde, water, and a small amount of light components undergoes a light component removal process to obtain light component product material and dilute formaldehyde recycling material. The light component product material contains at least one of methanol, methyl formate, dioxane, dioxane, ethylene oxide, benzene, cyclohexane, and methylal. The light component product material can be directly returned to the raw material formaldehyde preparation unit in the main production process of trioxymethylene as a raw material for formaldehyde production, or it can be used as a liquid fuel. The obtained dilute formaldehyde recycling material can be combined with the dilute formaldehyde raw material liquid and re-participated in the distillation and recovery process to further recover formaldehyde and trioxymethylene.

[0052] By utilizing a light component removal process, the light component impurities in the dilute formaldehyde material are further removed, improving the continuous stability of the method. This allows the dilute formaldehyde recycled material after light component removal to participate in the distillation and recovery process again, further improving the recovery efficiency and recovering the light component products, thereby further reducing the recovery cost.

[0053] In one specific embodiment, before the distillation and recovery process, the dilute aldehyde raw material liquid is further subjected to a first preheating treatment; wherein at least a portion of the dilute formaldehyde material is used as a heat source medium in the first preheating treatment to obtain cooled dilute formaldehyde material, and the cooled dilute formaldehyde material is subjected to a light removal treatment.

[0054] In one specific embodiment, at least a portion of the dilute formaldehyde material is used as a heat source medium in the distillation and recovery process;

[0055] In another specific embodiment, prior to the dehydration treatment, a second preheating treatment is performed on the heavy component material; wherein the wastewater material is used as a heat source medium in the second preheating treatment.

[0056] In another specific embodiment, at least a portion of the dilute formaldehyde material is used as a heat source medium to participate in the light-weight removal process, resulting in cooled dilute formaldehyde material, which is then subjected to light-weight removal treatment.

[0057] It is understandable that, since the dilute aldehyde raw material liquid produced in the main production process of trioxymethylene is at a low temperature, the dilute aldehyde raw material liquid is subjected to a first preheating treatment to reduce the heat demand in the distillation and recovery process; optionally, the discharge temperature after the first preheating treatment is 50-100℃; in order to make full use of the heat of the dilute formaldehyde material obtained from the dehydration treatment, at least part of the dilute formaldehyde material is used as a heat source medium to participate in the first preheating treatment to obtain cooled dilute formaldehyde material, and the cooled dilute formaldehyde material is then subjected to light removal treatment.

[0058] At least a portion of the dilute formaldehyde material is used as a heat source medium in the distillation and recovery process, thereby further recovering and utilizing the heat of the dilute formaldehyde material.

[0059] Since the dehydration process requires the separation of wastewater and formaldehyde, a large amount of heat is consumed during dehydration. This is also the only part of the recovery method that requires an external steam heat source. Therefore, performing a second preheating treatment on the heavy component material before dehydration can reduce the amount of steam required for dehydration and allow the wastewater obtained from dehydration to serve as a heat source medium for the second preheating treatment, further realizing the tiered utilization of heat and reducing heat consumption in the method. Optionally, the discharge temperature of the second preheating treatment is 130-180℃.

[0060] At least a portion of the dilute formaldehyde material is used as a heat source medium in the light-weight removal process to obtain cooled dilute formaldehyde material, which is then subjected to light-weight removal treatment; the heat of the dilute formaldehyde material is further recovered.

[0061] This invention reduces the heat requirements in the distillation recovery and dehydration processes through a first preheating treatment and a second preheating treatment. Furthermore, by using the dilute formaldehyde material obtained from dehydration to provide heat for the first preheating treatment, the recovery distillation treatment, and the light-weight material removal treatment, and by using the wastewater material to provide heat for the second preheating treatment, it achieves the tiered utilization of heat, greatly reduces the steam consumption of the recovery method, and further reduces energy consumption.

[0062] Furthermore, it also includes waste heat recovery treatment of at least a portion of the dilute formaldehyde material to obtain cooled dilute formaldehyde material, and then subjecting the cooled dilute formaldehyde material to light-weight removal treatment.

[0063] It is understandable that, in order to recover the excess heat of dilute formaldehyde materials, at least a portion of the dilute formaldehyde materials are subjected to waste heat recovery treatment to obtain steam or hot water, which can also be directly used to heat the equipment in the main production process of trioxymethylene, so that the cooled dilute formaldehyde materials after heat recovery can be subjected to light-weight removal treatment.

[0064] By utilizing waste heat recovery treatment, the heat of the dilute formaldehyde material is further recovered, reducing energy consumption.

[0065] Optionally, before the removal of light components, the cooled dilute formaldehyde material is further concentrated to obtain concentrated formaldehyde material and light component material, and the light component material is then subjected to the removal of light components.

[0066] The process involves cooling dilute formaldehyde material, which contains mostly formaldehyde, water, and a small amount of light components. This dilute formaldehyde material is then concentrated using a vacuum flash evaporation method to further concentrate the formaldehyde, resulting in concentrated formaldehyde and light component material. The light component material undergoes a further light component removal process to improve its purity. The concentrated formaldehyde material is then directly recycled back to the main trioxymethylene production process for refining, further increasing the concentration of recovered formaldehyde and reducing the amount of water introduced during recycling. This reduces water circulation over a large scale, thereby lowering the corresponding separation energy consumption.

[0067] In the concentration process, the cooled dilute formaldehyde material was further concentrated through simple vacuum distillation, which reduced the separation energy consumption caused by the large-scale circulation of water.

[0068] Optionally, the top pressure of the distillation recovery treatment is 0-0.1 MPaG, the top temperature is 70-120℃, and the bottom temperature is 80-130℃; the top pressure of the dehydration treatment is 0.6-2 MPaG, the top temperature is 160-200℃, and the bottom temperature is 170-210℃; the operating pressure of the concentration treatment is -0.095-0.1 MPaG; and the top pressure of the light component removal treatment is 0-0.1 MPaG, the top temperature is 50-100℃, and the bottom temperature is 60-110℃.

[0069] It is understandable that further limiting the execution parameters of each part of the recovery method can further improve the recovery efficiency of formaldehyde and trioxymethylene in dilute aldehydes.

[0070] On the other hand, the present invention also provides a dilute aldehyde recovery device for performing the above-described recovery method; Figure 1 A schematic diagram of a recycling device in a specific embodiment of the present invention is provided, as shown below. Figure 1 As shown, the recovery device includes a distillation recovery unit and a dehydration unit;

[0071] The distillation recovery unit 2 is provided with a first feed inlet, which is the inlet of the recovery device; the top outlet of the distillation recovery unit 2 is used to output trioxymethylene material, and the bottom outlet of the distillation recovery unit 2 is connected to the second feed inlet located in the dehydration unit 5.

[0072] The bottom outlet of dewatering unit 5 is used to discharge wastewater material, and the top outlet of dewatering unit is used to discharge dilute formaldehyde material.

[0073] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linkage" should be interpreted broadly. For example, they can refer to a fixed connection, a connection through an intermediate medium, or a connection within two elements or an interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0074] The distillation and recovery unit 2 is used to distill and recover the dilute aldehyde raw material liquid entering it, and to recover and separate most of the trioxymethylene, which is then recycled. The dehydration unit 5 is used to distill the heavy component material from the distillation and recovery unit 2, and to separate most of the water and acid components from the formaldehyde, thus recovering the formaldehyde for recycling.

[0075] Specifically, the dilute aldehyde feed liquid enters the recovery unit through the first inlet located in the distillation recovery unit 2, where it undergoes distillation recovery treatment to obtain trioxymethylene material and heavy component material. Most of the trioxymethylene and a small portion of formaldehyde are recovered and rise upwards, exiting the recovery unit from the top outlet of the distillation recovery unit 2 as trioxymethylene material output. The heavy component material separated by distillation descends and exits through the bottom outlet of the distillation recovery unit 2, then enters the dehydration unit 5 through the second inlet located in the dehydration unit 5 for dehydration treatment, resulting in dilute formaldehyde material and wastewater material. The acidic components and their salts descend along with a large amount of water and exit the recovery unit through the bottom outlet of the dehydration unit 5 as wastewater material for further wastewater treatment. The dilute formaldehyde material, mainly composed of formaldehyde, water, and a small amount of light components, rises and exits the recovery unit through the top outlet of the dehydration unit 5 as dilute formaldehyde material output, which can be recycled back into the main trioxymethylene production process for re-refining.

[0076] This invention provides a dilute aldehyde recovery device. A distillation unit recovers most of the paraformaldehyde and a small portion of the formaldehyde from the dilute aldehyde feedstock. A dehydration unit then recovers most of the remaining formaldehyde from the feedstock, removing wastewater, acidic components, and their salts. This prevents large amounts of water, acidic components, and their salts from returning to the main paraformaldehyde process and accumulating, thus improving the product quality of the paraformaldehyde and the stable operation of the device. The device recovers most of the paraformaldehyde and formaldehyde from the dilute aldehyde, achieving highly efficient recovery of dilute aldehydes.

[0077] In one specific embodiment, the distillation recovery unit 2 includes a plate column, a packed column, etc., and the theoretical number of plates in the distillation recovery unit 2 is 20-80; the dehydration unit 5 includes a plate column, and the theoretical number of plates in the dehydration unit 5 is 20-80.

[0078] The present invention does not limit the form of each unit. In one specific embodiment, the distillation recovery unit 2 is a distillation column and the dehydration unit 5 is a dehydration column.

[0079] Furthermore, Figure 2 A schematic diagram of a recycling device in a specific embodiment of the present invention is provided, as shown below. Figure 2 As shown, the recycling device also includes a light component removal unit 9; wherein, the top outlet of the dewatering unit 5 is also connected to the third feed inlet located in the light component removal unit 9, the top outlet of the light component removal unit 9 is used to output light component product material, and the bottom outlet of the light component removal unit 9 is connected to the first feed inlet.

[0080] The light component removal unit 9 is used to remove light component impurities from dilute formaldehyde material and further recover formaldehyde and trioxymethylene from the dilute formaldehyde. The dilute formaldehyde material from the top outlet of the dehydration unit 5 enters the light component removal unit 9 through the third inlet located therein, where it undergoes light component removal treatment. The light components are separated out by distillation, yielding light component product material and dilute formaldehyde recycling material. The light component product material ascends and exits the recovery unit through the top outlet of the light component removal unit 9, and can be directly returned to the formaldehyde preparation unit in the main trioxymethylene production process as a raw material for formaldehyde production, or used as a liquid fuel. The dilute formaldehyde recycling material descends and exits the light component removal unit 9 through the bottom outlet, then re-enters the distillation recovery unit 2 through the first inlet, participating again in the distillation recovery process to further recover formaldehyde and trioxymethylene.

[0081] In one specific embodiment, the light-removal unit 9 includes a plate tower, and the theoretical number of plates in the light-removal unit 9 is 20-80.

[0082] By using a light component removal unit, dilute formaldehyde material containing most formaldehyde, water, and a small amount of light components is treated to remove light components, resulting in light component product material. This material can be directly returned to the raw material formaldehyde preparation unit in the main production process of trioxymethylene as a raw material for formaldehyde production, or it can be used as a liquid fuel to further reduce costs. In addition, the dilute formaldehyde recycled material is re-entered into the distillation and recovery process to further recover formaldehyde and trioxymethylene.

[0083] In one specific embodiment, the light-removal unit 9 is a light-removal tower.

[0084] Optionally, Figure 3 A schematic diagram of a recycling device in a specific embodiment of the present invention is provided, as shown below. Figure 3 As shown, the recovery device also includes a first preheating unit 1, a second preheating unit 4, a waste heat recovery unit 7, a first reboiling unit 3, a second reboiling unit 6, and a third reboiling unit 10;

[0085] The material inlet of the first preheating unit 1 is the inlet of the recovery device, and the material outlet of the first preheating unit 1 is connected to the first feed inlet; the bottom outlet of the distillation recovery unit 2 is connected to the second feed inlet of the dehydration unit 5 via the second preheating unit 4, the bottom outlet of the distillation recovery unit 2 is connected to the material inlet of the second preheating unit 4, and the material outlet of the second preheating unit 4 is connected to the second feed inlet of the dehydration unit 5.

[0086] The bottom outlet of the distillation recovery unit 2 is also connected to the material inlet of the first reboiler unit 3, and the material outlet of the first reboiler unit 3 is connected to the lower reflux port of the distillation recovery unit 2; the bottom outlet of the dehydration unit 5 is also connected to the material inlet of the second reboiler unit 6, and the material outlet of the second reboiler unit 6 is connected to the lower reflux port of the dehydration unit 5; the bottom outlet of the light-light removal unit 9 is also connected to the material inlet of the third reboiler unit 10, and the material outlet of the third reboiler unit 10 is connected to the lower reflux port of the light-light removal unit 9.

[0087] The top outlet of the dehydration unit 5 is also connected to the heat medium inlet of the first preheating unit 1, the heat medium inlet of the first reboiling unit 3, the heat medium inlet of the third reboiling unit 10, and the heat medium inlet of the waste heat recovery unit 7, respectively. The heat medium outlet of the first preheating unit 1, the heat medium outlet of the distillation recovery unit 2, the heat medium outlet of the third reboiling unit 10, and the heat medium outlet of the waste heat recovery unit 7 are respectively connected to the third feed inlet of the light-light removal unit 9.

[0088] The bottom outlet of the dewatering unit 5 is connected to the heat medium inlet of the second preheating unit 4, and the heat medium outlet of the second preheating unit 4 is used to output wastewater material.

[0089] It is understandable that, due to the low temperature of the dilute aldehyde feed liquid produced in the main production process of trioxymethylene, the first preheating unit 1 is set up to preheat the dilute aldehyde feed liquid to reduce the processing difficulties caused by the excessively large reboiler of the distillation recovery unit 2 and reduce equipment investment; the second preheating unit 4 is used to preheat the heavy component material discharged from the bottom of the distillation recovery unit 2 to further reduce the steam demand of the dehydration unit and reduce the energy consumption of the unit; the waste heat recovery unit 7 is used to recover the heat of the dilute formaldehyde material at the top of the dehydration unit 5; the first reboiler unit 3 is used to provide a steam heat source for the distillation recovery unit 2; the second reboiler unit 6 is used to provide a steam heat source for the dehydration unit 5; and the third reboiler unit 10 is used to provide a steam heat source for the light component removal unit 9.

[0090] Specifically, the material inlet of the first preheating unit 1 is the inlet of the recovery device. The dilute aldehyde raw material liquid enters the recovery device through the material inlet of the first preheating unit 1 and undergoes the first preheating treatment in the first preheating unit, where its temperature rises. It then leaves the first preheating unit 1 through the material outlet of the first preheating unit 1 and enters the distillation recovery unit 2 through the first feed inlet of the distillation recovery unit 2, where it undergoes distillation recovery treatment. The heavy component material leaves the distillation recovery unit 2 through the bottom outlet of the distillation recovery unit 2 and enters the second preheating unit 4 through the material inlet of the second preheating unit 4, where it undergoes the second preheating treatment. After its temperature rises further, it leaves the second preheating unit 4 through the material outlet of the second preheating unit 4 and then enters the dehydration unit 5 through the second feed inlet of the dehydration unit 5, where it undergoes dehydration treatment.

[0091] After the heavy component material leaves through the bottom outlet of the distillation recovery unit 2, a portion of it enters the first reboiler unit 3 through the material inlet of the first reboiler unit 3. After undergoing reboilation treatment and phase change, it leaves the first reboiler unit 3 through the material outlet of the first reboiler unit 3 and re-enters the distillation recovery unit 2 through the lower reflux port of the distillation recovery unit 2 to participate in the distillation recovery treatment and further recover and refine the trioxymethylene.

[0092] The wastewater material obtained in the dehydration unit 5 leaves the dehydration unit 5 through the bottom outlet of the dehydration unit 5 and enters the second reboiler unit 6 through the material inlet of the second reboiler unit 6. After undergoing reboilation treatment and phase change, it leaves the second reboiler unit 6 through the material outlet of the second reboiler unit 6 and re-enters the dehydration unit 5 through the lower return port of the dehydration unit 5 to participate in the dehydration treatment and further recover the formaldehyde in it.

[0093] The dilute aldehyde recycled material obtained from the light aldehyde removal unit 9 leaves the light aldehyde removal unit 9 through the bottom outlet of the light aldehyde removal unit 9. Part of it enters the third reboiler unit 10 through the material inlet of the third reboiler unit 10. After undergoing reboil treatment and phase change in the third reboiler unit 10, it leaves the third reboiler unit 10 through the material outlet of the third reboiler unit 10 and re-enters the light aldehyde removal unit 9 through the lower reflux port of the light aldehyde removal unit 9 to participate in the light aldehyde removal treatment and further recover the dilute aldehyde.

[0094] After the dilute formaldehyde material is discharged through the top outlet of the dehydration unit 5, it enters each unit through the heat medium inlet of the first preheating unit 1, the heat medium inlet of the first reboiling unit 3, the heat medium inlet of the third reboiling unit 10, and the heat medium inlet of the waste heat recovery unit 7. In each unit, it serves as a heat source medium to heat each unit and recovers its own heat, thus reducing its own temperature. After the dilute formaldehyde material is cooled, it leaves each unit through the heat medium outlet of the first preheating unit 1, the heat medium outlet of the first reboiling unit 3, the heat medium outlet of the third reboiling unit 10, and the heat medium outlet of the waste heat recovery unit 7. Then, it enters the light-light removal unit 9 through the third feed inlet of the light-light removal unit 9 for light-light removal treatment.

[0095] After the wastewater material is discharged through the bottom outlet of the dewatering unit 5, it enters the second preheating unit 4 through the heat medium inlet of the second preheating unit 4, serving as a heat medium to heat the second preheating unit and recover the heat of the wastewater material. Then it is discharged through the heat medium outlet of the second preheating unit 4 for wastewater material output.

[0096] This invention reduces the heat demand in the distillation recovery unit and the dehydration unit by using a first preheating unit and a second preheating unit. Furthermore, by using the dilute formaldehyde material obtained from dehydration to provide heat to the first preheating unit, the recovery distillation unit, and the light odor removal unit, and by using the wastewater material to provide heat to the second preheating unit, it achieves the tiered utilization of heat, greatly reduces the steam consumption of the recovery method, and further reduces the energy consumption of the recovery device.

[0097] In one specific embodiment, the first preheating unit 1 is a heat exchanger, the second preheating unit 4 is a heat exchanger, the waste heat recovery unit 7 is a boiler or a shell and tube heat exchanger, the first reboiling unit 3 is a reboiler, the second reboiling unit 6 is a reboiler, and the third reboiling unit 10 is a reboiler.

[0098] Furthermore, Figure 4 A schematic diagram of a recycling device in a specific embodiment of the present invention is provided, as shown below. Figure 4 As shown, the recovery device also includes a concentration unit 8; wherein, the heat medium outlet of the first preheating unit 1, the heat medium outlet of the distillation recovery unit 2, the heat medium outlet of the third reboiling unit 10, and the heat medium outlet of the waste heat recovery unit 7 are respectively connected to the inlet of the concentration unit 8, and the top outlet of the concentration unit 8 is connected to the third feed inlet of the light removal unit 9; the bottom outlet of the concentration unit 8 is used to output concentrated formaldehyde material.

[0099] Concentration unit 8 is used to concentrate cooled dilute formaldehyde material by vacuum flash evaporation to further increase the formaldehyde concentration, reduce the moisture introduced when it is recycled back to the main production process of trioxymethylene, further reduce the moisture circulation over a large area, and thus reduce the corresponding separation energy consumption.

[0100] Specifically, after the dilute formaldehyde material provides heat to the first preheating unit 1, the first reboiling unit 3, the third reboiling unit 10, and the waste heat recovery unit 7, its own heat is recovered, resulting in cooled dilute formaldehyde material. This material first enters the concentration unit 8 through the inlet, where it undergoes concentration treatment. Through reduced pressure flash evaporation, the moisture and light components are removed, and the formaldehyde is further concentrated, resulting in light component material and concentrated formaldehyde material. The light component material, rich in moisture and light components, rises and leaves the concentration unit 8 through the top outlet, while the concentrated formaldehyde material leaves the recovery device through the bottom outlet of the concentration unit 8. As concentrated formaldehyde material output, it is directly recycled back to the main production process of trioxymethylene for refining, further increasing the concentration of recovered formaldehyde.

[0101] Through the concentration unit, the cooled dilute formaldehyde material was further concentrated using simple vacuum distillation, which further increased the formaldehyde concentration and reduced the separation energy consumption caused by the large-scale circulation of water.

[0102] In one specific embodiment, the concentration unit 8 is a flash evaporator.

[0103] It is understandable that, in order to further improve the recovery efficiency, the distillation recovery unit 2, the dehydration unit 5, and the light precipitate removal unit 9 are each equipped with a top condenser. The top material is condensed by the condenser and then refluxed. Optionally, the top reflux ratio of the distillation recovery unit 2 is 0.5-5, the top reflux ratio of the dehydration unit 5 is 0.5-5, and the top reflux ratio of the light precipitate removal unit 9 is 0.5-5. The reflux ratio refers to the ratio of the refluxed portion to the produced portion.

[0104] This invention provides a dilute aldehyde recovery device. A distillation unit recovers most of the paraformaldehyde and a small portion of the formaldehyde from the dilute aldehyde feedstock. A dehydration unit then recovers most of the remaining formaldehyde from the feedstock, removing wastewater, acidic components, and their salts. This prevents large amounts of water, acidic components, and their salts from returning to the main paraformaldehyde process and accumulating, thus improving the product quality of the paraformaldehyde and the stable operation of the device. The device recovers most of the paraformaldehyde and formaldehyde from the dilute aldehyde, achieving highly efficient recovery of dilute aldehydes.

[0105] The following detailed description of a method for recovering dilute aldehydes provided by the present invention is provided through specific embodiments.

[0106] Example 1

[0107] The dilute aldehyde raw material solution in this embodiment comprises: water: 74%; formaldehyde: 18%; trioxymethylene: 2%; light components: 5.5%; acidic components and their salts: 0.5%.

[0108] The method in this embodiment adopts... Figure 4 The recycling device shown performs the following steps:

[0109] (1) The dilute aldehyde raw material solution is mixed with sodium hydroxide solution to make the pH value of the dilute aldehyde raw material solution 6.8, and sent to the first preheating unit 1 (heat exchanger) for the first preheating treatment. After preheating, it is sent to the distillation recovery unit 2 (distillation column) through the first feed port for distillation recovery treatment to obtain trioxymethylene material and heavy component material. The trioxymethylene material is discharged from the top outlet of the distillation recovery unit 2 (distillation column), part of which is condensed and flows back into the distillation recovery unit 2 (distillation column), and the other part is collected as trioxymethylene material.

[0110] (2) The heavy component material is discharged through the bottom outlet of the distillation recovery unit 2 (distillation column) and sent to the second preheating unit 4 (heat exchanger) for second preheating treatment. After preheating, it enters the dehydration unit 5 (dehydration tower) through the second feed inlet for dehydration treatment to obtain dilute formaldehyde material and wastewater material. The dilute formaldehyde material is discharged through the top outlet of the dehydration unit 5 (dehydration tower). Part of the dilute formaldehyde material is condensed and flows back into the dehydration unit 5 (dehydration tower), and the other part of the dilute formaldehyde material leaves the dehydration unit 5 (dehydration tower). The wastewater material is discharged through the bottom outlet of the dehydration unit 5 (dehydration tower).

[0111] (3) The dilute formaldehyde material leaving the dehydration unit 5 (dehydration tower) is sent as a heat medium to the first preheating unit 1 (heat exchanger), the first reboiling unit 3 (heat exchanger), the third reboiling unit 10 (reboiler) and the waste heat recovery unit 7 (shell and tube heat exchanger) respectively. After providing heat to each unit, its own heat is recovered to obtain cooled dilute formaldehyde material. The wastewater material is sent as a heat medium to the second preheating unit 4 (heat exchanger). After providing heat to it, it is extracted as wastewater material. The heat of the second reboiling unit 6 (reboiler) is provided by steam generated by the heat generation equipment.

[0112] (4) The cooled dilute formaldehyde material is sent to the concentration system 8 (flash tank) for concentration treatment to obtain light component material and concentrated formaldehyde material; the concentrated formaldehyde material is extracted from the bottom outlet of the concentration system 8 (flash tank);

[0113] (5) The light component material is discharged from the top outlet of the concentration system 8 (flash tank) and sent to the light component removal unit 9 (light component removal tower) through the third feed port for light component removal treatment to obtain light component product material and dilute aldehyde circulating material; the light component material is discharged from the top outlet of the light component removal unit 9 (light component removal tower), part of the light component product material is condensed and flows back into the light component removal unit 9 (light component removal tower), and the other part is collected as light component product material; the dilute aldehyde circulating material is discharged from the bottom outlet of the light component removal unit 9 (light component removal tower), and after merging with the dilute aldehyde raw material liquid, it re-enters the first preheating unit 1 (heat exchanger) for recovery.

[0114] The discharge temperature of the first preheating treatment is 90℃;

[0115] The theoretical number of plates in the distillation recovery unit is 60; the reflux ratio is 2.2, the top temperature is 110℃, the bottom temperature is 120℃, and the top pressure is 0.01MPaG.

[0116] The discharge temperature of the second preheating treatment is 140℃;

[0117] The theoretical number of plates in the dehydration unit is 44; the reflux ratio is 1.4, the top temperature is 170℃, the bottom temperature is 120℃, and the top pressure is 0.7MPaG.

[0118] The pressure of the concentration system is -0.06 MPaG;

[0119] The theoretical number of plates in the light-duty removal unit is 52; the reflux ratio is 1, the top temperature is 60℃, the bottom temperature is 80℃, and the top pressure is 0.002MPaG.

[0120] The recovery rate of trioxymethylene in the trioxymethylene material was 99.7%; the mass percentage of water in the wastewater material was 99.9%; the mass percentage of acidic components and their salts in the dilute formaldehyde material was 22 ppm; and the mass percentage of formaldehyde in the concentrated formaldehyde material was 52%.

[0121] The mass composition of the dilute aldehyde recycling material includes water: 89%; formaldehyde: 8.3%; paraformaldehyde: 2.5%; and light components: 0.2%.

[0122] The production of 1 ton of polyoxymethylene product requires 6.2 tons of steam.

[0123] Example 2

[0124] The difference between this embodiment and Embodiment 1 is that:

[0125] The dilute aldehyde raw material solution consists of water: 82%; formaldehyde: 13%; paraformaldehyde: 1.5%; light components: 3.4%; acidic components and their salts: 0.1%.

[0126] The discharge temperature of the first preheating treatment is 95℃;

[0127] The theoretical number of plates in the distillation recovery unit is 55; the reflux ratio is 3, the top temperature is 95℃, the bottom temperature is 105℃, and the top pressure is 0.001MPaG.

[0128] The discharge temperature of the second preheating treatment is 125℃;

[0129] The theoretical number of plates in the dehydration unit is 65; the reflux ratio is 1, the top temperature is 180℃, and the top pressure is 1.0MPaG.

[0130] The pressure of the concentration system is -0.08 MPaG;

[0131] The theoretical number of plates in the light-duty removal unit is 40; the reflux ratio is 3, the top temperature is 82℃, the bottom temperature is 95℃, and the top pressure is 0.03MPaG.

[0132] In this embodiment, the recovery rate of trioxymethylene in the trioxymethylene material is 99.7%; the mass percentage of water in the wastewater material is 99.8%; the mass percentage of acidic components and their salts in the dilute formaldehyde material is 14 ppm; and the mass percentage of formaldehyde in the concentrated formaldehyde material is 48%.

[0133] The mass composition of the dilute aldehyde recycling material includes water: 91%; formaldehyde: 7%; paraformaldehyde: 1.9%; and light components: 0.1%.

[0134] The production of 1 ton of polyoxymethylene product requires 7 tons of steam.

[0135] Example 3

[0136] The difference between this embodiment and embodiment 1 is that step (4) is not performed; in this embodiment, the amount of steam consumed is 6.8 tons for every ton of polyoxymethylene product produced.

[0137] Comparative Example 1

[0138] The difference between this comparative example and Example 1 is that only step (1) is performed. In this example, the heavy component material includes water: 86.7885%; formaldehyde: 10.5%; trioxymethylene: 0.0015%; light component: 2.6%; acidic component and its salt: 0.11%. Since the heavy component material contains a lot of formaldehyde, it is difficult to process it directly.

[0139] Comparative Example 2

[0140] The difference between this comparative example and Example 1 is that in step (1), sodium hydroxide is not added to the dilute aldehyde raw material solution, and the pH value of the dilute aldehyde raw material solution is 6.0; in this example, obvious corrosion and leakage occurred in the distillation recovery unit.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering dilute aldehydes, characterized in that, Includes the following steps: Step 1: Add a neutralizing agent to the dilute aldehyde raw material solution and mix to make the pH value of the dilute aldehyde raw material solution 6.2-6.8; Step 2: Perform a first preheating treatment on the dilute aldehyde raw material solution; Step 3: The preheated dilute aldehyde raw material liquid is subjected to distillation recovery treatment to obtain trioxymethylene material and heavy component material; the top pressure of the distillation recovery treatment is 0-0.1 MPaG, the top temperature is 70-120℃, and the bottom temperature is 80-130℃. Step 4: Perform a second preheating treatment on the recombinant material, and then dehydrate the preheated recombinant material to obtain dilute formaldehyde material and wastewater material; the top pressure of the dehydration treatment is 0.6-2 MPaG, the top temperature is 160-200℃, and the bottom temperature is 170-210℃; wherein, at least a portion of the dilute formaldehyde material is used as a heat source medium in the first preheating treatment to obtain cooled dilute formaldehyde material; and the wastewater material is used as a heat source medium in the second preheating treatment; Step 5: Perform waste heat recovery treatment on at least a portion of the dilute formaldehyde material to obtain cooled dilute formaldehyde material; Step 6: The cooled dilute formaldehyde material is concentrated by vacuum flash evaporation to obtain concentrated formaldehyde material and light component material; the operating pressure of the concentration treatment is -0.095-0.1 MPaG; Step 7: Perform a light component removal treatment on the light component material to obtain light component product material and dilute aldehyde recycling material, so that the dilute aldehyde recycling material can participate in the distillation recovery treatment again; the top pressure of the light component removal treatment is 0-0.1 MPaG, the top temperature is 50-100℃, and the bottom temperature is 60-110℃.

2. The recycling method according to claim 1, characterized in that, At least a portion of the dilute formaldehyde material is used as a heat source medium in the distillation and recovery process; and / or, At least a portion of the dilute formaldehyde material is used as a heat source medium in the removal of light elements to obtain the cooled dilute formaldehyde material, which is then subjected to the removal of light elements.

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