A process for the low temperature production of formaldehyde

Abstract

The application discloses a method for producing formaldehyde at low temperature, and belongs to the technical field of formaldehyde production. The method comprises the following steps: preparing a high-efficiency catalyst by taking iron nitrate nonahydrate, ammonium molybdate tetrahydrate and lithium hydride as raw materials; feeding mixed gas of methanol and air into a reactor filled with the high-efficiency catalyst under the condition that the temperature is 250-280 DEG C; and collecting gas at the outlet of the reactor to complete the method for producing formaldehyde at low temperature. The embedding of lithium can expand the crystal lattices of the catalytic products, thereby generating a large number of oxygen vacancies, enhancing the electron-donating capacity, and enabling the adsorption of p-formaldehyde to be quickly dissociated and the active sites to be quickly reduced at a relatively low temperature, so that the activity of subsequent catalysis is ensured. The plasma treatment can increase the surface area and the number of active sites of the high-efficiency catalyst, and further improve the catalytic activity. The method for producing formaldehyde at low temperature can improve the conversion rate of methanol and the yield of formaldehyde at a relatively low temperature, and is helpful to reduce energy consumption and reduce the volatilization of Mo.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde production technology, specifically relating to a method for producing formaldehyde at low temperatures. Background Technology

[0002] Formaldehyde is an organic compound, the simplest aliphatic aldehyde, with the chemical formula HCHO or CH2O and a molecular weight of 30.03. It is a colorless gas with a pungent odor, irritating to the eyes and nose. Formaldehyde is readily soluble in water and ethanol; the concentration of its aqueous solution can reach up to 55%, but is typically 35%-40%, usually 37%, known as formaldehyde solution or formalin. Formaldehyde is also a reducing agent with strong reducing properties, especially in alkaline solutions. It is used in dyeing, explosives, and plastics industries, and is also an important disinfectant and preservative.

[0003] In nature, wherever protein exists, formaldehyde will inevitably be present, as formaldehyde is one of the decomposition products of protein. In contemporary society, formaldehyde has become one of the most important and widely used bulk basic organic chemical raw materials. Formaldehyde production methods include direct hydrocarbon oxidation, catalytic oxidation with dimethyl ether, and methanol-air oxidation. The direct hydrocarbon oxidation method has low yields and complex processes, and is therefore less commonly used. The catalytic oxidation with dimethyl ether method has also been phased out with the development of the methanol-air oxidation method. Therefore, methanol has become the main raw material for formaldehyde production.

[0004] Formaldehyde production from methanol typically uses either iron-molybdenum catalysts or silver catalysts. Silver catalysts are prone to poisoning, and the yield of formaldehyde and the conversion rate of methanol produced by the silver method are not as high as those of the iron-molybdenum method. Even though the iron-molybdenum method has a higher production system cost, it is still used by some companies. The reaction temperature for formaldehyde production via the iron-molybdenum method is generally between 250-350℃. The higher the temperature, the better the formaldehyde yield and other technical indicators. However, at high temperatures, the molybdenum in the iron-molybdenum catalyst is prone to sublimation, which can lead to catalyst deactivation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing formaldehyde at low temperatures. By improving the iron-molybdenum catalyst, the iron-molybdenum catalyst can maintain high catalytic activity at lower reaction temperatures, thereby reducing the volatilization of Mo.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for producing formaldehyde at low temperature includes the following steps:

[0008] A highly efficient catalyst is loaded into the reactor, and methanol and air are mixed into a mixed gas with a volume fraction of 6-8% at 80-90℃. Then, at 250-280℃, the mixture is accelerated at a rate of 180-200m³. 3A gas flow rate of / min is used to introduce mixed gas into the reactor, and the gas at the reactor outlet is collected to complete the method of low-temperature formaldehyde production.

[0009] Furthermore, the highly efficient catalyst is prepared through the following steps:

[0010] Step 1: Add ferric nitrate nonahydrate, ammonium molybdate tetrahydrate, lithium hydride, and an ethanol aqueous solution with a mass fraction of 25-50% to the reactor. After stirring and dissolving, add the carbonization support, ultrasonically disperse, and then vacuum-seal and let stand for 20-24 hours. Filter the mixture and keep the filter cake at 300-320℃ for 2.5-3 hours. Then raise the temperature to 440-460℃ and keep it at that temperature for 1.5-2 hours. Allow it to cool naturally, wash it 2-3 times with deionized water, and dry it to obtain the pre-prepared catalyst powder.

[0011] Step 2: Transfer the pre-prepared catalyst powder to a radio frequency plasma system, evacuate the system and introduce hydrogen and nitrogen gas mixed in a 1:1 volume ratio, and treat the plasma at 200-220W and 18-20sccm for 40-60 minutes to obtain plasma-treated catalyst powder; mix the plasma catalyst powder and binder at a mass ratio of 100:0.1-0.5, wet and granulate with anhydrous ethanol, and then mold into ring-shaped high-efficiency catalyst.

[0012] Furthermore, the ratio of ferric nitrate nonahydrate, ammonium molybdate tetrahydrate, lithium hydride, ethanol solution, and carbonization carrier is 404g: 530-618g: 3-3.5g: 1200-1500mL: 500-600g.

[0013] Furthermore, the binder includes, but is not limited to, guar gum powder, magnesium stearate, and hydroxypropyl methylcellulose.

[0014] Furthermore, the carbonization support is prepared through the following steps:

[0015] Step 1: Add soluble sugar and 2% ferric nitrate solution to the reaction vessel, stir and mix, and react at 180-200℃ for 6-8 hours. After natural cooling, filter the mixture, wash the filter cake with deionized water 3-5 times, and vacuum dry to obtain pre-carbonized powder.

[0016] Step 2: Disperse the pre-carbonized powder in deionized water to form a dispersion with a mass fraction of 10-12% and transfer it to a reaction vessel. Then, add hexadecyltetramethylammonium bromide and sodium hydroxide to the reaction vessel, stir and mix, and then add tetraethyl orthosilicate. Continue stirring at 200-500 r / min for 2-4 h, filter, wash the filter cake with deionized water 3-5 times, vacuum dry, and carbonize at 480-520℃ for 2.5-3 h under nitrogen protection. After natural cooling, obtain carbonized powder. Etch the carbonized powder with 10% hydrofluoric acid for 10-20 min, wash the filter cake with deionized water 3-5 times, and vacuum dry to obtain the carbonized support.

[0017] Furthermore, the ratio of soluble sugar to ferric nitrate solution is 3g:10mL.

[0018] Furthermore, the soluble sugar is sucrose, fructose, or glucose.

[0019] Furthermore, the ratio of the dispersion, hexadecyltetramethylammonium bromide, sodium hydroxide, and tetraethyl orthosilicate is 110-120 mL: 0.28-0.3 g: 0.04 g: 1.5 mL.

[0020] The beneficial effects of this invention are:

[0021] The present invention provides a method for producing formaldehyde at low temperatures, which uses a high-efficiency catalyst instead of a conventional iron-molybdenum catalyst. This method can improve the conversion rate of methanol and the yield of formaldehyde at relatively low temperatures, and helps to reduce energy consumption and reduce the volatilization of Mo. It has important prospects for improving the economic benefits of formaldehyde production by the iron-molybdenum process.

[0022] In the process of preparing high-efficiency catalysts, soluble sugars are used as carbon sources, and hexadecyltetramethylammonium bromide and tetraethyl orthosilicate are mixed into the pre-carbonized powder as hard template agents, which helps to improve the stability of the carbonized support, thereby maintaining the openness of the micropores, which helps to load the catalyst and ensure the throughput of methanol gas.

[0023] Ferric nitrate nonahydrate and ammonium molybdate tetrahydrate are converted into catalytically active products such as Fe2(MoO4)3 after high-temperature treatment. Lithium hydride is also added during the preparation of the pre-catalyst powder, increasing lithium content compared to conventional iron-molybdenum catalysts. The lithium intercalation causes lattice expansion of these catalytically active products, generating numerous oxygen vacancies and enhancing electron-donating capabilities. This allows the highly efficient catalyst to rapidly dissociate formaldehyde adsorption at lower temperatures, quickly reducing active sites and ensuring the activity of subsequent catalytic processes. Plasma treatment can increase the surface area and number of active sites of the highly efficient catalyst, further improving its catalytic activity. Detailed Implementation

[0024] 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.

[0025] Example 1: This example provides a method for producing formaldehyde at low temperature, including the following steps:

[0026] Step 1: Add 30 kg of sucrose and 100 L of 2% ferric nitrate solution to the reactor. After stirring and mixing, react at 180 °C for 6 h. After natural cooling, filter the mixture. Wash the filter cake three times with deionized water and dry it under vacuum to obtain pre-carbonized powder.

[0027] Step 2: Disperse the pre-carbonized powder in 1100L of deionized water to form a 10% (w / w) dispersion and transfer it to a reactor. Then, add 2.8kg of hexadecyltetramethylammonium bromide and 0.4kg of sodium hydroxide to the reactor, stir and mix, and then add 15L of tetraethyl orthosilicate. Continue stirring at 200r / min for 2h, filter, wash the filter cake three times with deionized water, vacuum dry, and carbonize at 480℃ for 2.5h under nitrogen protection. After natural cooling, obtain carbonized powder. Etch the carbonized powder with 10% (w / w) hydrofluoric acid for 10min, wash the filter cake three times with deionized water, and vacuum dry to obtain the carbonized support.

[0028] Step 3: Add 4.04 kg of ferric nitrate nonahydrate, 5.3 kg of ammonium molybdate tetrahydrate, 0.03 kg of lithium hydride, and 12 L of 25% ethanol aqueous solution to the reactor. After stirring and dissolving, add 5 kg of carbonized support, ultrasonically disperse, vacuum and let stand for 20 h, filter, keep warm at 300℃ for 2.5 h, then raise the temperature to 440℃ and keep warm for 1.5 h, cool naturally, wash twice with deionized water, and dry to obtain the pre-prepared catalyst powder.

[0029] Step 4: Transfer the pre-prepared catalyst powder to the radio frequency plasma system, evacuate and introduce hydrogen and nitrogen mixed in a 1:1 volume ratio, and treat with plasma at 200W and 18sccm for 40 minutes to obtain plasma catalyst powder; mix the plasma catalyst powder and guar powder in a mass ratio of 100:0.1, wet and granulate with anhydrous ethanol, and then mold into a ring-shaped high-efficiency catalyst.

[0030] Step 5: The high-efficiency catalyst is loaded into the reactor, with a filling length of 100cm. Methanol and air are mixed at 80℃ to form a 6% (by volume) mixed gas. Then, at 250℃, the mixture is accelerated at a rate of 180m... 3 A gas flow rate of / min is used to introduce mixed gas into the reactor, and the gas at the reactor outlet is collected to complete the method of low-temperature formaldehyde production.

[0031] Example 2: This example provides a method for producing formaldehyde at low temperature, including the following steps:

[0032] Step 1: Add 30 kg of fructose and 100 L of 2% ferric nitrate solution to the reactor. After stirring and mixing, react at 190 °C for 7 h. After natural cooling, filter the mixture. Wash the filter cake four times with deionized water and dry it under vacuum to obtain pre-carbonized powder.

[0033] Step 2: Disperse the pre-carbonized powder in 1150 L of deionized water to form a dispersion with a mass fraction of 11%, and transfer it to a reactor. Then, add 2.9 kg of hexadecyltetramethylammonium bromide and 0.4 kg of sodium hydroxide to the reactor, stir and mix, and then add 15 L of tetraethyl orthosilicate. Continue stirring at 350 r / min for 3 h, filter, wash the filter cake with deionized water 4 times, vacuum dry, and carbonize at 500 °C for 2.8 h under nitrogen protection. After natural cooling, carbonized powder is obtained. The carbonized powder is etched with 10% hydrofluoric acid for 15 min, the filter cake is washed with deionized water 4 times, and vacuum dried to obtain the carbonized support.

[0034] Step 3: Add 4.04 kg of ferric nitrate nonahydrate, 5.8 kg of ammonium molybdate tetrahydrate, 0.032 kg of lithium hydride, and 13.5 L of 40% ethanol aqueous solution to the reactor. After stirring and dissolving, add 5.5 kg of carbonized support, ultrasonically disperse, vacuum and let stand for 22 h, filter, keep warm at 310℃ for 2.8 h, then raise the temperature to 450℃ and keep warm for 1.8 h, cool naturally, wash twice with deionized water, and dry to obtain the pre-prepared catalyst powder.

[0035] Step 4: Transfer the pre-prepared catalyst powder to the radio frequency plasma system, evacuate and introduce hydrogen and nitrogen mixed in a 1:1 volume ratio, and treat with plasma at 210W and 19sccm for 50 minutes to obtain plasma catalyst powder; mix the plasma catalyst powder and guar gum powder in a mass ratio of 100:0.3, wet and granulate with anhydrous ethanol, and then mold into a ring-shaped high-efficiency catalyst.

[0036] Step 5: The high-efficiency catalyst is loaded into the reactor, with a filling length of 100cm. Methanol and air are mixed at 85℃ to form a 7% (by volume) mixed gas. Then, at 265℃, the mixture is accelerated at a rate of 190m... 3 A gas flow rate of / min is used to introduce mixed gas into the reactor, and the gas at the reactor outlet is collected to complete the method of low-temperature formaldehyde production.

[0037] Example 3: This example provides a method for producing formaldehyde at low temperature, including the following steps:

[0038] Step 1: Add 30 kg of glucose and 100 L of 2% ferric nitrate solution to the reactor. After stirring and mixing, react at 200 °C for 8 h. After natural cooling, filter the mixture. Wash the filter cake 5 times with deionized water and dry it under vacuum to obtain pre-carbonized powder.

[0039] Step 2: Disperse the pre-carbonized powder in 1200L of deionized water to form a 12% (w / w) dispersion and transfer it to a reactor. Then, add 3kg of hexadecyltetramethylammonium bromide and 0.4kg of sodium hydroxide to the reactor, stir and mix, and then add 15L of tetraethyl orthosilicate. Continue stirring at 500r / min for 4h, filter, wash the filter cake 5 times with deionized water, vacuum dry, carbonize at 520℃ for 3h under nitrogen protection, and allow to cool naturally to obtain carbonized powder. Etch the carbonized powder with 10% (w / w) hydrofluoric acid for 20min, wash the filter cake 5 times with deionized water, and vacuum dry to obtain the carbonized support.

[0040] Step 3: Add 4.04 kg of ferric nitrate nonahydrate, 6.18 kg of ammonium molybdate tetrahydrate, 0.035 kg of lithium hydride, and 15 L of 50% ethanol aqueous solution to the reactor. After stirring and dissolving, add 6 kg of carbonized support, ultrasonically disperse, vacuum and let stand for 24 h, filter, keep warm at 320℃ for 3 h, then raise the temperature to 460℃ and keep warm for 2 h, cool naturally, wash three times with deionized water, and dry to obtain the pre-prepared catalyst powder.

[0041] Step 4: Transfer the pre-prepared catalyst powder to the radio frequency plasma system, evacuate and introduce hydrogen and nitrogen mixed in a 1:1 volume ratio, and treat with plasma at 220W and 20sccm for 60 minutes to obtain plasma catalyst powder; mix the plasma catalyst powder and guar gum powder in a mass ratio of 100:0.5, wet and granulate with anhydrous ethanol, and then mold into a ring-shaped high-efficiency catalyst.

[0042] Step 5: The high-efficiency catalyst is loaded into the reactor, with a filling length of 100cm. Methanol and air are mixed at 90℃ to form a mixed gas with a volume fraction of 8%. Then, at 280℃, the mixture is accelerated at a rate of 200m... 3 A gas flow rate of / min is used to introduce mixed gas into the reactor, and the gas at the reactor outlet is collected to complete the method of low-temperature formaldehyde production.

[0043] Comparative Example 1: Based on Example 3, lithium hydride was not added in step three, while the remaining steps remained unchanged, thus completing the method for producing formaldehyde at low temperature.

[0044] Comparative Example 2: Based on Example 3, step four does not involve radio frequency plasma system treatment; the pre-prepared catalyst powder is directly prepared into a ring-shaped catalyst, while the remaining steps remain unchanged, thus completing the low-temperature formaldehyde production method.

[0045] Comparative Example 3: Based on Example 3, the raw material of the high-efficiency catalyst was replaced with Clariant's commercially available iron-molybdenum catalyst (elemental composition: Fe, Mo, O), while the remaining steps remained unchanged, to complete the low-temperature formaldehyde production method.

[0046] The physical parameters of the high-efficiency catalysts in the examples and comparative examples were unified as follows: outer diameter of the ring 5.0 mm, inner diameter of the ring 2.5 mm, height 3.0 mm; bulk density 0.86 ± 0.01 g / cm³. 3 .

[0047] Test examples 1-3 and comparative examples 1-3 were performed to test the indicators, and the methanol-to-chlorine conversion, reaction selectivity, and formaldehyde yield were recorded. The results are shown in Table 1.

[0048] Table 1

[0049] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 reaction temperature 250℃ 265℃ 280℃ 280℃ 280℃ 280℃ Methanol conversion rate 98.52％ 98.65％ 98.93％ 97.43％ 97.96％ 97.88％ Reaction selectivity 97.4％ 97.6％ 98.5％ 95.5％ 96.3％ 96.3％ Formaldehyde yield 93.1％ 93.5％ 93.8％ 91.2％ 92.6％ 92.5％

[0050] As can be seen from Table 1, after using a high-efficiency catalyst in Examples 1-3, the relevant indicators for formaldehyde production were better under conditions of lower production temperature than conventional conditions. This indicates that the addition of lithium hydride and the use of radio frequency plasma system treatment both help to improve the low-temperature catalytic efficiency of the iron-molybdenum catalyst.

[0051] It should be noted that, in this document, terms such as “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.

[0052] 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 method for producing formaldehyde at low temperature, characterized in that, Includes the following steps: A highly efficient catalyst is loaded into the reactor, and methanol is mixed with air at 80-90℃ to form a mixed gas with a volume fraction of 6-8%. The mixture is then subjected to a reaction at 250-280℃, with a flow rate of 180-200m³. 3 A gas flow rate of / min is used to introduce mixed gas into the reactor, and the gas at the reactor outlet is collected to complete the method of low-temperature formaldehyde production. The high-efficiency catalyst is prepared by the following steps: Step 1: Add ferric nitrate nonahydrate, ammonium molybdate tetrahydrate, lithium hydride and 25-50 wt% ethanol aqueous solution to the reactor, stir to dissolve, add carbonization support, ultrasonically disperse, vacuum and let stand for 20-24 hours, filter, keep the filter cake at 300-320℃ for 2.5-3 hours, at 440-460℃ for 1.5-2 hours, cool naturally, wash and dry to obtain pre-prepared catalyst powder; Step 2: Transfer the pre-prepared catalyst powder to the radio frequency plasma system, evacuate, and introduce hydrogen and nitrogen gas mixed in a 1:1 volume ratio. Treat the plasma at 200-220W and 18-20sccm for 40-60 minutes to obtain plasma-treated catalyst powder. Mix the plasma catalyst powder and binder at a mass ratio of 100:0.1-0.5, wet and granulate with anhydrous ethanol, and mold into ring-shaped high-efficiency catalyst. The ratio of the amounts of ferric nitrate nonahydrate, ammonium molybdate tetrahydrate, lithium hydride, ethanol solution, and carbonization support is 404g: 530-618g: 3-3.5g: 1200-1500mL: 500-600g. The carbonized support is prepared through the following steps: The pre-carbonized powder was dispersed in deionized water to form a dispersion of 10-12 wt%. Then, hexadecyltetramethylammonium bromide and sodium hydroxide were added and stirred. After mixing, tetraethyl orthosilicate was added and stirred at 200-500 r / min for 2-4 h. The mixture was then filtered, washed, and dried. It was then carbonized at 480-520℃ for 2.5-3 h under nitrogen protection and natural cooling to obtain carbonized powder. The powder was then etched with 10 wt% hydrofluoric acid for 10-20 min, washed, and dried to obtain the carbonized support. The pre-carbonized powder is prepared by the following steps: Soluble sugar and 2% ferric nitrate solution were added to the reaction vessel. After stirring and mixing, the mixture was reacted at 180-200℃ for 6-8 hours. After natural cooling, the mixture was filtered, washed, and dried to obtain pre-carbonized powder. Soluble sugars include sucrose, fructose, or glucose.

2. The method for producing formaldehyde at low temperature according to claim 1, characterized in that, The binder includes guar gum powder, magnesium stearate, and hydroxypropyl methylcellulose.

3. The method for producing formaldehyde at low temperature according to claim 1, characterized in that, The ratio of the dispersion, hexadecyltetramethylammonium bromide, sodium hydroxide, and tetraethyl orthosilicate is 110-120 mL: 0.28-0.3 g: 0.04 g: 1.5 mL.

4. The method for producing formaldehyde at low temperature according to claim 1, characterized in that, The ratio of soluble sugar to ferric nitrate solution is 3g:10mL.