A method for producing formaldehyde by recovering water vapor

Abstract

The application discloses a kind of preparation methods for recovering water vapor production formaldehyde, belong to formaldehyde production technical field, comprising the following steps: chemical reduction is loaded nano silver on porous carrier, and composite silver catalyst is obtained;Methanol, air and water vapor are mixed, preheating is formed methanol-air-water vapor ternary gas, and ternary gas is carried out methanol dehydrogenation oxidation reaction under the catalytic condition of composite silver catalyst, and methanol mixed gas is generated, and formaldehyde aqueous solution is obtained by cooling, dilution.The process for producing formaldehyde in the application has better selectivity, and the methanol conversion rate is higher.Compared with conventional impregnation method, the size of nano silver particles loaded on the catalyst obtained by chemical reduction and loading nano silver is smaller and more uniform, which can reduce the reaction temperature and effectively prevent a large amount of silver sintering, thereby improving the service life of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde production technology, specifically relating to a method for producing formaldehyde by recovering water vapor. Background Technology

[0002] Formaldehyde is an important basic organic chemical raw material with a wide range of applications. Depending on the raw material, its production methods can be categorized as follows: ① Non-catalytic oxidation using liquefied petroleum gas (LPG); ② Dimethyl ether oxidation; ③ Methane oxidation; ④ Methanol-air oxidation. Based on the process, methanol-air oxidation is further divided into silver-catalyzed oxidation (excess methanol method) and iron-molybdenum oxide-catalyzed oxidation (excess air method), etc. The silver-catalyzed formaldehyde process has advantages over the iron-molybdenum method, such as lower investment and lower power consumption, and is widely used. However, the silver-catalyzed formaldehyde process has disadvantages such as higher methanol consumption per unit volume, higher methanol content in the formaldehyde product, and lower formaldehyde concentration.

[0003] Furthermore, the silver process operates at temperatures above 600°C, causing silver particles to easily fuse and enlarge. Combined with its sensitivity to poisons, this leads to catalyst deactivation. Additionally, conventional silver process catalysts exhibit low selectivity for formaldehyde, readily generating byproducts. These factors, along with catalyst lifespan and regeneration issues, limit its industrial application. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing formaldehyde by recovering water vapor, so as to solve the problem of high catalytic temperature in the silver process for formaldehyde production.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for producing formaldehyde by recovering water vapor includes the following steps:

[0007] Nanoparticles of silver were chemically reduced on a porous support to obtain a composite silver catalyst. Methanol, air, and water vapor were mixed and preheated to form a methanol-air-water vapor ternary gas. The ternary gas was subjected to the dehydrogenation reaction of methanol under the catalytic conditions of the composite silver catalyst to generate a formaldehyde mixture. After cooling and dilution, a formaldehyde aqueous solution was obtained.

[0008] As a preferred embodiment of the present invention, chemically reducing and loading silver nanoparticles on a porous support includes the following steps:

[0009] The porous support was added to deionized water and ultrasonically dispersed. Then, silver ammonia solution was added and stirred at 40°C. After the reaction was completed, glucose aqueous solution was added dropwise. After the addition was completed, the temperature was kept constant and stirring was continued. After filtration, washing with water and drying, the composite silver catalyst was obtained.

[0010] As a preferred embodiment of the present invention, the porous carrier is prepared by the following steps:

[0011] Imidazole organic ligands were reacted with copper salts to obtain metal salt complexes. The metal salt complexes, glucose, and organosilicon resin were added to anhydrous ethanol and mixed. A foaming agent and a pore-forming agent were added, and the mixture was poured into a mold. Under nitrogen protection, the mixture was heated to 250°C and cured for 7 hours. Then, it was heated to 600°C and carbonized in a nitrogen stream for 3 hours. Finally, it was calcined at 1250-1450°C. After calcination, it was kept at that temperature for 2 hours, then cooled to 600°C and kept at that temperature for 4 hours. Finally, it was cooled to room temperature to obtain a porous carrier.

[0012] As a preferred embodiment of the present invention, the copper salt includes either copper nitrate or copper chloride.

[0013] As a preferred embodiment of the present invention, the ratio of the metal salt complex, glucose and organosilicon resin is 5g:0.5mol:20g; the molar ratio of copper salt and azole organic ligand is 1:2-6.

[0014] As a preferred embodiment of the present invention, the azole organic ligands include one or more of imidazole, 2-methylimidazolium, benzimidazole and 1H-1,2,3-triazole.

[0015] As a preferred embodiment of the present invention, the molar ratio of methanol to air is 1:1.5-3.

[0016] As a preferred embodiment of the present invention, the preheating temperature is 120-140℃.

[0017] As a preferred embodiment of the present invention, the catalyst has a catalytic temperature range of 580-700℃.

[0018] As a preferred technical solution of the present invention, the formaldehyde mixture produced is used to generate steam by recovering waste heat, which is then used as the raw material for ternary gas.

[0019] The beneficial effects of this invention are:

[0020] This invention provides a method for producing formaldehyde by recovering water vapor. By adding a self-made catalyst, the catalyst is not sensitive to reaction parameters. The porous support (porous silicon carbide ceramic particles) used for the catalyst has good high temperature resistance. The catalyst has a wide operating temperature range, high flexibility, and is easy to control in production. It is suitable for industrial production. Correspondingly, the temperature of the catalytic reaction is reduced, the catalyst's resistance to sintering is improved, and its service life is greatly extended.

[0021] The formaldehyde production process in this invention exhibits better selectivity and a higher methanol conversion rate. Compared to conventional impregnation methods, the catalyst obtained by chemical reduction and loading of nano-silver has smaller and more uniform nano-silver particles, which can effectively prevent the sintering of large amounts of silver while lowering the reaction temperature, thereby improving the catalyst's lifespan.

[0022] To further improve catalytic selectivity, this invention provides a porous support. This porous support uses a metal salt complex as a dopant, glucose as a carbon source, and organosilicon resin as a silicon source. Appropriate amounts of foaming agent and pore-forming agent are added, and the mixture is sintered at high temperature to obtain the porous support. The main component of this porous support is silicon carbide. A synergistic catalytic effect is achieved between the doped copper and the in-situ generated nano-silver, improving the selectivity of formaldehyde and further increasing the conversion rate of methanol. The porous support prepared by this invention (mainly silicon carbide) not only has a large specific surface area to support more active material particles, but also exhibits good high-temperature resistance. More importantly, silicon carbide possesses excellent thermal conductivity. Its good mass and heat transfer properties prevent backmixing and allow for rapid heat transfer during the reaction, thus ensuring temperature uniformity during the reaction process. This maintains high activity and high selectivity during the reaction, laying the foundation for further improving the catalyst and enhancing its catalytic activity. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] This embodiment provides a method for producing formaldehyde by recovering water vapor, comprising the following steps:

[0026] A composite silver catalyst was obtained by chemically reducing and loading silver nanoparticles onto a porous support. 50 mg of the porous support was added to 50 mL of deionized water and ultrasonically dispersed. Then, 5 mL of silver ammonia solution was added, and the mixture was stirred at 40 °C for 1 h. After the addition was complete, 10 mL of 1 mol / L glucose aqueous solution was added dropwise. The temperature was maintained, and stirring continued for 1 h. The resulting product was filtered, washed with water, and dried to obtain the composite silver catalyst. The silver ion concentration in the silver ammonia solution was approximately 0.1 mol / L. The porous support was porous silicon carbide ceramic particles.

[0027] Methanol, air, and water vapor are mixed and preheated to form a methanol-air-water vapor ternary gas mixture at 120°C; the molar ratio of methanol to air is 1:2.8. The ternary gas mixture undergoes a methanol dehydrogenation reaction under a composite silver catalyst to produce a formaldehyde mixture. After cooling and dilution, an aqueous formaldehyde solution is obtained. The catalytic temperature for the dehydrogenation reaction is 580°C. The produced formaldehyde mixture is used to recover waste heat to produce water vapor, which is then used as a raw material for the ternary gas mixture.

[0028] Example 2

[0029] This embodiment provides a method for producing formaldehyde by recovering water vapor, comprising the following steps:

[0030] A composite silver catalyst was obtained by chemically reducing and loading silver nanoparticles onto a porous support. 50 mg of the porous support was added to 50 mL of deionized water and ultrasonically dispersed. Then, 5 mL of silver ammonia solution was added, and the mixture was stirred at 50 °C for 1 h. After stirring, 10 mL of a 1 mol / L glucose aqueous solution was added dropwise. The temperature was maintained, and stirring continued for 1 h. The resulting product was filtered, washed with water, and dried to obtain the composite silver catalyst. The silver ion concentration in the silver ammonia solution was approximately 0.1 mol / L. The porous support was porous silicon carbide ceramic particles.

[0031] Methanol, air, and water vapor are mixed and preheated to form a methanol-air-water vapor ternary gas mixture at 130°C; the molar ratio of methanol to air is 1:1.6. The ternary gas mixture undergoes a methanol dehydrogenation reaction under a composite silver catalyst to produce a formaldehyde mixture. After cooling and dilution, an aqueous formaldehyde solution is obtained. The catalytic temperature for the dehydrogenation reaction is 690°C. The produced formaldehyde mixture is used to recover waste heat to produce water vapor, which is then used as a raw material for the ternary gas mixture.

[0032] Example 3

[0033] This embodiment provides a method for producing formaldehyde by recovering water vapor, comprising the following steps:

[0034] A composite silver catalyst was obtained by chemically reducing and loading silver nanoparticles onto a porous support. 50 mg of the porous support was added to 50 mL of deionized water and ultrasonically dispersed. Then, 5 mL of silver ammonia solution was added, and the mixture was stirred at 45 °C for 1 h. After stirring, 10 mL of 1 mol / L glucose aqueous solution was added dropwise. The temperature was maintained, and stirring continued for 1 h. The resulting product was filtered, washed with water, and dried to obtain the composite silver catalyst. The silver ion concentration in the silver ammonia solution was approximately 0.1 mol / L. The porous support was porous silicon carbide ceramic particles.

[0035] Methanol, air, and water vapor are mixed and preheated to form a methanol-air-water vapor ternary gas mixture at 140°C; the molar ratio of methanol to air is 1:2.5. The ternary gas mixture undergoes a methanol dehydrogenation reaction under a composite silver catalyst to produce a formaldehyde mixture. After cooling and dilution, an aqueous formaldehyde solution is obtained. The catalytic temperature for the dehydrogenation reaction is 650°C. The produced formaldehyde mixture is used to recover waste heat to produce water vapor, which is then used as a feedstock for the ternary gas mixture.

[0036] Comparative Example 1

[0037] Compared with Example 1, this comparative example replaces the chemical reduction and loading of silver nanoparticles with a conventional impregnation method. Specifically, the porous support is impregnated in a 1 mol / L silver nitrate aqueous solution for 2 hours. After impregnation, it is removed, dried at 110°C, and calcined at 600°C for 4 hours to obtain the catalyst. The remaining raw material ratios and preparation process are the same as in Example 1.

[0038] The methanol conversion and formaldehyde selectivity in Examples 1-3 and Comparative Example 1 were recorded, as well as the catalyst stabilization time. The results are shown in Table 1 below:

[0039] Table 1

[0040] Sample Methanol conversion rate / % Formaldehyde selectivity / % Example 1 96.23 92.55 Example 2 95.95 92.12 Example 3 96.10 92.11 Comparative Example 1 87.21 84.05

[0041] The test results show that the formaldehyde production process in this invention exhibits better selectivity and a higher methanol conversion rate. Compared with the conventional impregnation method, the catalyst obtained by chemical reduction and loading of nano-silver has smaller and more uniform nano-silver particles, which can effectively prevent the sintering of large amounts of silver while lowering the reaction temperature, thereby improving the catalyst's lifespan.

[0042] Example 4

[0043] This embodiment differs from Example 1 in that the porous carrier is different, but the remaining raw material ratios and preparation process remain the same as in Example 1. Specifically:

[0044] 2-Methylimidazole and copper nitrate were reacted to obtain a metal salt complex. The metal salt complex, glucose, and organosilicon resin were added to anhydrous ethanol (the amount of anhydrous ethanol added was sufficient to ensure that all raw materials were mixed evenly) and stirred. A foaming agent and a pore-forming agent were added, and the mixture was poured into a mold. Under nitrogen protection, the mixture was heated to 250°C and cured for 7 hours. Then, it was heated to 600°C and carbonized in a nitrogen stream for 3 hours. Then, it was calcined at the reaction temperature (1250°C, 1300°C, 1350°C, 1400°C, and 1450°C, with a heating rate of 10°C / min). After calcination, it was held at the temperature for 2 hours, then cooled to 600°C and held at the temperature for 4 hours. Finally, it was cooled to room temperature to obtain a porous carrier. The amount of silicone resin (RSN-6018, Dow Corning) and foaming agent (azodicarbonamide) added was 2% of the total raw material amount, and the amount of pore-forming agent (polymethyl methacrylate microspheres (PMMA, particle size range 40-60 μm) added was 1% of the total raw material amount). The ratio of metal salt complex, glucose and silicone resin was 5 g: 0.5 mol: 20 g; the molar ratio of copper nitrate and 2-methylimidazole was 1:2. The remaining raw material ratios and preparation process were the same as in Example 1.

[0045] Example 5

[0046] This embodiment differs from Example 1 in that the porous carrier is different, but the remaining raw material ratios and preparation process remain the same as in Example 1. Specifically:

[0047] Benzimidazole and copper nitrate were reacted to obtain a metal salt complex. The metal salt complex, glucose, and organosilicon resin were added to anhydrous ethanol (the amount of anhydrous ethanol added was sufficient to ensure that all raw materials were mixed evenly) and stirred. A foaming agent and a pore-forming agent were added, and the mixture was poured into a mold. Under nitrogen protection, the mixture was heated to 250°C and cured for 7 hours. Then, it was heated to 600°C and carbonized in a nitrogen stream for 3 hours. Then, it was calcined at the reaction temperature (1250°C, 1300°C, 1350°C, 1400°C, and 1450°C, with a heating rate of 10°C / min). After calcination, it was held at the temperature for 2 hours, then cooled to 600°C and held at the temperature for 4 hours. Finally, it was cooled to room temperature to obtain a porous carrier. The addition amount of silicone resin (RSN-6018, Dow Corning) and foaming agent (azodicarbonamide) is 2% of the total raw material amount, and the addition amount of pore-forming agent (polymethyl methacrylate microspheres (PMMA, particle size range 40-60 μm)) is 1% of the total raw material amount. The ratio of metal salt complex, glucose and silicone resin is 5g:0.5mol:20g; the molar ratio of copper nitrate and benzimidazole is 1:4.

[0048] Example 6

[0049] This embodiment differs from Example 1 in that the porous carrier is different, but the remaining raw material ratios and preparation process remain the same as in Example 1. Specifically:

[0050] 2-Methylimidazole and copper nitrate were reacted to obtain a metal salt complex. The metal salt complex, glucose, and organosilicon resin were added to anhydrous ethanol (the amount of anhydrous ethanol added was sufficient to ensure that all raw materials were mixed evenly) and stirred. A foaming agent and a pore-forming agent were added, and the mixture was poured into a mold. Under nitrogen protection, the mixture was heated to 250°C and cured for 7 hours. Then, it was heated to 600°C and carbonized in a nitrogen stream for 3 hours. Then, it was calcined at the reaction temperature (1250°C, 1300°C, 1350°C, 1400°C, and 1450°C, with a heating rate of 10°C / min). After calcination, it was held at the temperature for 2 hours, then cooled to 600°C and held at the temperature for 4 hours. Finally, it was cooled to room temperature to obtain a porous carrier. The addition amount of silicone resin (RSN-6018, Dow Corning), foaming agent (azodicarbonamide) is 2% of the total raw material amount, and the addition amount of pore-forming agent (polymethyl methacrylate microspheres (PMMA, particle size range 40-60 μm) is 1% of the total raw material amount). The ratio of metal salt complex, glucose and silicone resin is 5g:0.5mol:20g; the molar ratio of copper nitrate and 2-methylimidazole is 1:6.

[0051] The methanol conversion rate and formaldehyde selectivity in Examples 1-3 and Comparative Example 1 were recorded, and the results are shown in Table 2 below:

[0052] Table 2

[0053] Sample Methanol conversion rate / % Formaldehyde selectivity / % Example 4 99.12 98.56 Example 5 98.95 98.35 Example 6 99.02 98.42

[0054] The test results show that the self-made catalyst used in this invention can still ensure high conversion rate and selectivity at a relatively low catalytic temperature (580℃).

[0055] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A production method of recovering water vapor to produce formaldehyde, characterized by, The method comprises the following steps: The silver catalyst is prepared by loading nano-silver on a porous carrier through chemical reduction, and the catalyst is used to catalyze the dehydrogenation and oxidation of methanol in a methanol-air-water vapor ternary gas to generate a formaldehyde mixture gas, which is cooled and diluted to obtain a formaldehyde aqueous solution; the catalytic temperature of the catalyst ranges from 580 to 700 DEG C; The silver catalyst is prepared by loading nano-silver on a porous carrier through chemical reduction, and the catalyst is used to catalyze the dehydrogenation and oxidation of methanol in a methanol-air-water vapor ternary gas to generate a formaldehyde mixture gas, which is cooled and diluted to obtain a formaldehyde aqueous solution; the catalytic temperature of the catalyst ranges from 580 to 700 DEG C; The metal salt complex is prepared by reacting an imidazole organic ligand and a copper salt, and then the metal salt complex, glucose and an organic silicon resin are mixed and stirred in anhydrous ethanol, a foaming agent and a pore-forming agent are added, and then the mixture is poured into a mold, heated to 250 DEG C for 7 h under nitrogen protection, carbonized at 600 DEG C for 3 h under nitrogen flow, and then calcined at 1250-1450 DEG C for 2 h after cooling to room temperature to obtain a porous carrier; The porous carrier is added to deionized water and ultrasonically dispersed, and then a silver ammonia solution is added, and after stirring at 40 DEG C, a glucose aqueous solution is added dropwise, and after the dropwise addition is completed, the temperature is kept unchanged, and the stirring is continued, and then the composite silver catalyst is obtained after filtration, water washing and drying; the imidazole organic ligand includes one or more of imidazole, 2-methyl imidazole, benzimidazole and 1H-1,2,3-triazole.

2. A process for the preparation of formaldehyde from recovered water vapor according to claim 1, characterized in that, The copper salt includes one of copper nitrate or copper chloride.

3. A process for the preparation of formaldehyde from recovered water vapor according to claim 1, characterized in that, The amount ratio of the metal salt complex, glucose and organic silicon resin is 5 g:0.5 mol:20 g; and the molar ratio of the copper salt and the imidazole organic ligand is 1:2-6.

4. The method of claim 1, wherein the water vapor is recovered from a water vapor generator. The molar ratio of methanol to air is 1:1.5-3.

5. The method of claim 1, wherein the water vapor is recovered from a water vapor generator. The preheating temperature is 120-140 DEG C.

6. The method of claim 1, wherein the water vapor is recovered from a water vapor stream produced in a process for producing formaldehyde. The produced formaldehyde mixture gas is recovered to produce water vapor as a raw material of the ternary gas. The silver catalyst is prepared by loading nano-silver on a porous carrier through chemical reduction, and the catalyst is used to catalyze the dehydrogenation and oxidation of methanol in a methanol-air-water vapor ternary gas to generate a formaldehyde mixture gas, which is cooled and diluted to obtain a formaldehyde aqueous solution; the catalytic temperature of the catalyst ranges from 580 to 700 DEG C;