Iron-molybdenum catalyst and application thereof in preparation of formaldehyde

Abstract

The invention discloses an iron-molybdenum catalyst and application thereof in preparation of formaldehyde, and belongs to the technical field of chemical engineering, the iron-molybdenum catalyst comprises active metal, an organic phosphoric acid modifier and a carrier, and the application of the iron-molybdenum catalyst in synthesis of formaldehyde is provided. The catalyst keeps high strength, high activity and high stability, the phenomenon of bed blockage caused by catalyst pulverization is avoided, the catalyst is not easy to inactivate, the production cost is reduced, the production efficiency of formaldehyde is improved, and large-scale production is facilitated.

Description

Technical Field

[0001] The present application belongs to the field of chemical technology, and in particular, relates to an iron-molybdenum catalyst and its application in the preparation of formaldehyde. Background Art

[0002] As an important organic chemical raw material and chemical intermediate, formaldehyde is widely used in many fields such as chemical industry, materials, and medicine. According to a global market survey, the output of formaldehyde in 2020 was 45.6 metric tons, and it is expected to further increase at an annual rate of 4.65% during the period 2021-2028, reaching a market value of US$37.7 billion by 2028. At the same time, my country has become the world's largest producer and consumer of formaldehyde, with formaldehyde production capacity accounting for 55% of the global total production capacity and consumption accounting for 53%. Among the existing formaldehyde production processes in China, the main one is methanol oxidation process, which is divided into "silver method" and "iron-molybdenum method" according to the type of catalyst used. The silver catalyst process has a long history. Its advantages are mature technology, short process, low power consumption, low investment, and large single-series production capacity; its disadvantages are high methanol consumption, short catalyst life, and poor activity.

[0003] Compared with the "silver method", the "iron-molybdenum method" has the advantages of lower reaction temperature, lower methanol consumption, longer catalyst service life, and the ability to produce high-concentration formaldehyde solutions. However, the iron-molybdenum catalyst method cannot be equipped with a methanol recovery tower, and requires a large amount of air to ensure the safe operation of the device (1 mol of methanol vapor requires 13 mol of air). The presence of a large amount of air makes all the equipment and pipelines of the device much larger than those of the silver method, increasing equipment investment and poor economic benefits. In addition, the iron-molybdenum catalyst used is one of the most difficult catalysts to prepare. The catalysts used in the domestic iron-molybdenum process are still heavily dependent on foreign imports, which has caused inconvenience and restrictions on the further application of the iron-molybdenum formaldehyde process in China.

[0004] However, traditional silver catalysts have short service life, are easily poisoned and deactivated, require pretreatment of raw materials, have high requirements for equipment, low catalyst activity, and poor reaction selectivity. The main component of the iron-molybdenum catalyst is Fe(MoO4)3·MoO3. During the production process, the oxidation reaction mainly takes place on the catalyst surface. When methanol reacts with oxygen on the catalyst surface, formaldehyde is generated and leaves the catalyst surface. The oxygen entering the reaction system is replenished to the catalyst surface to re-form an active catalyst. During process operation, if the oxygen content in the system is lower than 4.5%, the oxidized metal catalyst will be reduced, and the catalyst activity will be irreversibly reduced, resulting in low methanol conversion rate and low formaldehyde yield in the later operation.

[0005] Therefore, it is particularly important to seek new process methods and new catalytic technologies for formaldehyde synthesis in order to improve catalyst efficiency and formaldehyde yield, promote its industrial development, and consolidate and enhance the comprehensive competitiveness of products. Summary of the invention

[0006] The purpose of the implementation of the present application is to provide an iron-molybdenum catalyst and its application in the preparation of formaldehyde, so as to solve the technical problems existing in the prior art that the iron-molybdenum catalyst is difficult to prepare, the catalyst is unstable, and the catalytic efficiency is low.

[0007] To achieve the above purpose, the technical solution adopted in this application is: to provide an iron-molybdenum catalyst prepared by the following method: (i) dispersing an organophosphoric acid modifier into water in a reaction container, adding a carrier and stirring to obtain a mixture; (ii) adding an iron source and a molybdenum source to the mixture and mixing; stirring while keeping warm, removing excess solvent, and drying to obtain an iron-molybdenum catalyst.

[0008] In one embodiment, The organic phosphoric acid modifier in step (i) is one or more of aminotrimethylenephosphonic acid (NTMP, CAS: 6419-19-8), ethylenediaminetetramethylenephosphonic acid (EDTMP, CAS: 1429-50-1), diethylenetriaminepentamethylenephosphonic acid (DTPMP, CAS: 15827-60-8), aminomethylphosphonic acid (AMP, CAS: 1066-51-9), hydroxymethylphosphonic acid (HMP, CAS: 2617-47-2), and iminodimethylenephosphonic acid (IDMP, CAS: 17261-34-6).

[0009] In one embodiment, Step (i) The carrier is one or more of zinc oxide (ZnO), cerium oxide (CeO2), silicon dioxide (SiO2), zirconium dioxide (ZrO2), and aluminum oxide (Al2O3).

[0010] In one embodiment, In step (i), the mass ratio of the organophosphate modifier to the carrier is 0.1-1:1.

[0011] In one embodiment, In step (i), the temperature of the reaction vessel is 40-80°C, and the stirring time is 1-3 h.

[0012] In one embodiment, In step (ii), the iron source is selected from one or more of iron-containing hydrochlorides, sulfates, nitrates, acetylacetonates and hydrates thereof; more specifically, the iron source is one or more of ferric chloride hexahydrate (FeCl3·6H2O), ferric nitrate (Fe(NO3)3), ferrous sulfate (FeSO4), ferric chloride (FeCl3), ferrous chloride (FeCl2), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), ferrous sulfate heptahydrate (FeSO4·7H2O), ammonium ferric sulfate dodecahydrate (NH4Fe(SO4)2·12H2O), ferric sulfate (Fe2(SO4)3) or ferric triacetylacetonate (Fe(acac)3); the molybdenum source is selected from one or more of ammonium molybdate, sodium molybdate, molybdenum acetylacetonate, sodium molybdate dihydrate and hydrated sodium dodecamolybdate phosphate; more specifically, the molybdenum source is ammonium molybdate ((NH4)2MoO4), ammonium tetramolybdate ((NH4)2Mo4O 13 ·2H2O), ammonium heptamolybdate ((NH4)6Mo7O 24 ·4H2O), sodium molybdate (Na2MoO4), sodium molybdate dihydrate (Na2MoO4·2H2O), molybdenum acetylacetonate (MoO6(acac)2) or sodium phosphomolybdate (Na3PO4·12MoO3) or one or more thereof.

[0013] In one embodiment, The mass ratio of the iron source to the carrier is 0.01-0.05:1, and the mass ratio of the iron source to the molybdenum source in step (ii) is 1:1-5.

[0014] In one embodiment, The temperature of step (ii) is 40-60°C and the time is 2-6 h.

[0015] The present application also provides an application of an iron-molybdenum catalyst in the preparation of formaldehyde, which is to use the iron-molybdenum catalyst of any of the above embodiments, add the iron-molybdenum catalyst into a fixed bed reactor, introduce gas, and use methanol as a raw material for oxidation reaction to prepare formaldehyde.

[0016] In one embodiment, The gas is oxygen or air, preferably air, the air pressure is normal pressure, and the volume space velocity of the gas is 1000-3000 h -1 , to meet the reaction requirements, not limited here; the reaction temperature is 200-300 ° C; the methanol feed rate is 10-30 ml / min.

[0017] The present application provides an iron-molybdenum catalyst and provides its application in synthesizing formaldehyde. Compared with the prior art, the present application has the following beneficial effects: 1. The novel iron-molybdenum catalyst provided by the present application is prepared by an impregnation method, and the preparation method is simple. The catalyst comprises an active metal, an organic phosphoric acid modifier and a carrier; the organic phosphoric acid modifier is uniformly covered on the surface of the catalyst, and forms a complex with the active metal ion through a coordination bond, which not only improves the activity of the catalyst, but also effectively reduces the loss of active components during the reaction, so that the catalyst obtains high activity and high stability; 2. The reaction temperature of the system is reduced in formaldehyde synthesis, and a highly selective conversion of methanol to formaldehyde is achieved under relatively mild conditions, side reactions at high temperatures are suppressed, and the reaction selectivity and yield are improved; in summary, the technical solution of the present application has a moderate reaction temperature, few side reactions, and the catalyst maintains high strength, high activity and high stability, avoiding the phenomenon of bed blockage caused by catalyst pulverization, making the catalyst less likely to deactivate, reducing production costs, improving production efficiency, and facilitating large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 This is an electron microscope photo of the iron-molybdenum catalyst magnified 50 times; Figure 2 This is an electron microscope photograph of the iron-molybdenum catalyst magnified 200 times. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] After the reaction is completed, the reaction liquid in the receiving bottle is collected, and the formaldehyde is analyzed and determined according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution".

[0022]

[0023]

[0024] Example 1 (i) Add 50 ml of deionized water and 7.0 g of DTPMP to a reaction container, then add 10.0 g of CeO2, raise the temperature to 60 °C, keep stirring for 2 h, then cool to 40 °C to obtain a mixture; (ii) Add 1.452 g of FeCl3·6H2O and 1.839 g of (NH4)2MoO4 to the mixture, keep it at 40℃ and stir it for 4 h, then remove the excess water by rotary evaporation, and dry it to obtain an iron-molybdenum catalyst, which is recorded as catalyst #1 and is ready for use. The structural characterization is shown in Figure 1-2 As shown, instrument model: JEOL JSM-6701F; The catalyst No. 1 was pressed into tablets with a mesh size of 20-60 and then added to the fixed bed reactor. At room temperature, the air volumetric velocity was 2000 h -1 , raise the temperature to 200 ℃, keep warm for 1 hour, start feeding methanol liquid phase at a flow rate of 20 ml / min, and after 2 hours of reaction, analyze and determine the formaldehyde and methanol solution in the receiving bottle according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution". The methanol conversion rate is 63.4% and the formaldehyde selectivity is 98.7%.

[0025] Example 2 The difference between this embodiment and embodiment 1 is that after adding catalyst #1 into the fixed bed reactor, the temperature is raised to 300°C, and the other operations are the same. The methanol conversion rate is 65.8% and the formaldehyde selectivity is 96.2%.

[0026] Example 3 The difference between this embodiment and embodiment 1 is that the methanol liquid phase feed rate is 10 ml / min, and the other operations are the same. The methanol conversion rate is 67.3% and the formaldehyde selectivity is 97.5%.

[0027] Example 4 The difference between this embodiment and embodiment 1 is that the methanol liquid phase feed rate is 30 ml / min, and the other operations are the same. The methanol conversion rate is 59.4%, and the formaldehyde selectivity is 98.3%.

[0028] Example 5 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 2.59 g of NH4Fe(SO4)2·12H2O to prepare catalyst #2, and the remaining operations are the same. The methanol conversion rate is 63.8% and the formaldehyde selectivity is 98.1%.

[0029] Example 6 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 1.493 g of FeSO4·7H2O to prepare catalyst #3, and the remaining operations are the same. The methanol conversion rate is 63.2% and the formaldehyde selectivity is 98.3%.

[0030] Example 7 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 2.148 g of Fe2(SO4)3 to prepare catalyst #4, and the remaining operations are the same. The methanol conversion rate is 63.0% and the formaldehyde selectivity is 98.4%.

[0031] Example 8 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 0.871 g of FeCl3 to prepare catalyst #5, and the remaining operations are the same. The methanol conversion rate is 63.5% and the formaldehyde selectivity is 98.7%.

[0032] Example 9 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 2.170 g of Fe(NO3)3·9H2O to prepare catalyst #6, and the remaining operations are the same. The methanol conversion rate is 62.8% and the formaldehyde selectivity is 98.2%.

[0033] Example 10 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 0.681 g of FeCl2 to prepare catalyst #7, and the remaining operations are the same. The methanol conversion rate is 62.8% and the formaldehyde selectivity is 98.2%.

[0034] Embodiment 11 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 1.897 g of Fe(acac)3 to prepare catalyst #8, and the remaining operations are the same. The methanol conversion rate is 62.5%, and the formaldehyde selectivity is 98.3%.

[0035] Example 12 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 6.228 g of (NH4)2Mo4O 13 ·2H2O to obtain catalyst 9#. The rest of the operations were the same, the methanol conversion rate was 65.1%, and the formaldehyde selectivity was 97.8%.

[0036] Embodiment 13 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 11.593 g of (NH4)6Mo7O 24 ·4H2O to obtain catalyst 10#. The rest of the operations were the same, the methanol conversion rate was 63.4%, and the formaldehyde selectivity was 98.1%.

[0037] Embodiment 14 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 1.932 g of Na2MoO4 to prepare catalyst #11, and the remaining operations are the same. The methanol conversion rate is 64.2% and the formaldehyde selectivity is 98.4%.

[0038] Embodiment 15 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 2.270 g of Na2MoO4·2H2O to prepare catalyst #12, and the other operations are the same. The methanol conversion rate is 63.2% and the formaldehyde selectivity is 98.3%.

[0039] Example 16 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 3.060 g of MoO6(acac)2 to prepare catalyst #13, and the remaining operations are the same. The methanol conversion rate is 63.6% and the formaldehyde selectivity is 97.6%.

[0040] Embodiment 17 The difference between this embodiment and embodiment 8 is that in step (ii), (NH4)2MoO4 is replaced by 17.741 g of Na3PO4·12MoO3 to prepare catalyst #14, and the remaining operations are the same. The methanol conversion rate is 63.4% and the formaldehyde selectivity is 97.2%.

[0041] Embodiment 18 The difference between this embodiment and embodiment 8 is that in step (i), CeO2 is replaced by ZnO to obtain catalyst #15, and the remaining operations are the same. The methanol conversion rate is 60.7% and the formaldehyde selectivity is 97.5%.

[0042] Embodiment 19 The difference between this embodiment and embodiment 8 is that in step (i), CeO2 is replaced by SiO2 to obtain catalyst #16, and the remaining operations are the same. The methanol conversion rate is 61.2% and the formaldehyde selectivity is 97.1%.

[0043] Embodiment 20 The difference between this embodiment and embodiment 8 is that in step (i), CeO2 is replaced by ZrO2 to obtain catalyst #17, and the remaining operations are the same. The methanol conversion rate is 60.7% and the formaldehyde selectivity is 97.6%.

[0044] Embodiment 21 The difference between this embodiment and embodiment 8 is that in step (i), CeO2 is replaced by Al2O3 to obtain catalyst #18, and the remaining operations are the same. The methanol conversion rate is 62.5% and the formaldehyde selectivity is 97.4%.

[0045] Embodiment 22 The difference between this embodiment and embodiment 8 is that in step (i), DTPMP is replaced by NTMP to prepare catalyst #19, and the remaining operations are the same. The methanol conversion rate is 62.8% and the formaldehyde selectivity is 97.8%.

[0046] Embodiment 23 The difference between this embodiment and embodiment 8 is that in step (i), DTPMP is replaced by EDTMP to prepare catalyst #20, and the remaining operations are the same. The methanol conversion rate is 63.1% and the formaldehyde selectivity is 98.5%.

[0047] Embodiment 24 The difference between this embodiment and embodiment 8 is that in step (i), DTPMP is replaced by AMP to obtain catalyst #21, and the remaining operations are the same. The methanol conversion rate is 63.0% and the formaldehyde selectivity is 98.0%.

[0048] Embodiment 25 The difference between this embodiment and embodiment 8 is that in step (i), DTPMP is replaced by IDMP to obtain catalyst #22, and the remaining operations are the same. The methanol conversion rate is 63.2% and the formaldehyde selectivity is 98.1%.

[0049] Embodiment 26 The difference between this embodiment and embodiment 8 is that in step (i), DTPMP is replaced by HMP to obtain catalyst #23, and the remaining operations are the same. The methanol conversion rate is 62.4%, and the formaldehyde selectivity is 97.4%.

[0050] Embodiment 27 The difference between this embodiment and embodiment 8 is that in step (i), after adding CeO2, the temperature is raised to 40°C to obtain catalyst #24, and the remaining operations are the same. The methanol conversion rate is 60.3% and the formaldehyde selectivity is 97.6%.

[0051] Embodiment 28 The difference between this embodiment and embodiment 8 is that in step (i), after adding CeO2, the temperature is raised to 80°C to prepare 25# catalyst, and the other operations are the same. The methanol conversion rate is 65.4% and the formaldehyde selectivity is 97.1%.

[0052] Embodiment 29 The difference between this embodiment and embodiment 8 is that in step (i), the temperature is raised and then stirred for 1 hour to obtain catalyst #26. The remaining operations are the same. The methanol conversion rate is 59.4% and the formaldehyde selectivity is 98.0%.

[0053] Embodiment 30 The difference between this embodiment and embodiment 8 is that in step (i), the temperature is raised and then stirred for 3 hours to obtain catalyst #27. The remaining operations are the same. The methanol conversion rate is 64.3% and the formaldehyde selectivity is 98.2%.

[0054] Embodiment 31 The difference between this embodiment and embodiment 8 is that in step (i), after keeping warm and stirring for 2 hours, the temperature is lowered to 50°C to obtain catalyst #28, and the other operations are the same. The methanol conversion rate is 62.1%, and the formaldehyde selectivity is 97.0%.

[0055] Embodiment 32 The difference between this embodiment and embodiment 8 is that in step (i), after the stirring for 2 h, no cooling treatment is performed to obtain catalyst #29. The other operations are the same, and the methanol conversion rate is 61.3%, and the formaldehyde selectivity is 96.4%.

[0056] Embodiment 33 The difference between this embodiment and embodiment 8 is that in step (ii), the mixture is kept at 50°C and stirred for 2 h to obtain catalyst #30. The remaining operations are the same, and the methanol conversion rate is 61.2% and the formaldehyde selectivity is 97.0%.

[0057] Embodiment 34 The difference between this embodiment and embodiment 8 is that in step (ii), the temperature is kept at 60°C and stirred for 6 hours to obtain catalyst #31. The other operations are the same. The methanol conversion rate is 65.7% and the formaldehyde selectivity is 98.4%.

[0058] Embodiment 35 The difference between this embodiment and embodiment 8 is that in step (ii), the mass of (NH4)2MoO4 is 0.613 g, and 32# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 63.1%, and the formaldehyde selectivity is 98.1%.

[0059] Embodiment 36 The difference between this embodiment and embodiment 8 is that in step (ii), the mass of (NH4)2MoO4 is 3.065 g, and catalyst #33 is obtained. The remaining operations are the same, and the methanol conversion rate is 64.7%, and the formaldehyde selectivity is 99.0%.

[0060] Embodiment 37 The difference between this embodiment and embodiment 8 is that in step (i), the mass of DTPMP is 1.0 g, and 34# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 60.0%, and the formaldehyde selectivity is 96.4%.

[0061] Embodiment 38 The difference between this embodiment and embodiment 8 is that in step (i), the mass of DTPMP is 5.0 g, and 35# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 61.2%, and the formaldehyde selectivity is 97.8%.

[0062] Embodiment 39 The difference between this embodiment and embodiment 8 is that in step (i), the mass of DTPMP is 10.0 g, and 36# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 65.8%, and the formaldehyde selectivity is 98.9%.

[0063] Embodiment 40 The difference between this embodiment and embodiment 8 is that in step (ii), the mass of FeCl3 is 0.29 g, the mass of (NH4)2MoO4 is 0.613 g, and 37# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 60.7% and the formaldehyde selectivity is 97.3%.

[0064] Embodiment 41 The difference between this embodiment and embodiment 8 is that in step (ii), the mass of FeCl3 is 1.452 g, the mass of (NH4)2MoO4 is 3.065 g, and 38# catalyst is obtained. The other operations are the same, and the methanol conversion rate is 66.2% and the formaldehyde selectivity is 98.5%.

[0065] Embodiment 42 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 0.816 g of FeSO4 to prepare catalyst #39, and the remaining operations are the same. The methanol conversion rate is 63.2% and the formaldehyde selectivity is 98.3%.

[0066] Embodiment 43 The difference between this embodiment and embodiment 1 is that in step (ii), FeCl3·6H2O is replaced by 1.299 g of Fe2(NO3)3 to prepare catalyst #40, and the remaining operations are the same. The methanol conversion rate is 62.7% and the formaldehyde selectivity is 98.2%.

[0067] Comparative Example 1 (i) Add 7.0 g of DTPMP to 50 ml of deionized water, then add 10.0 g of CeO2, raise the temperature to 60 °C, keep stirring for 2 h, then cool to 40 °C to obtain a mixture; (ii) Add 0.871 g of FeCl3, keep warm and stir for 4 h, then remove excess water by rotary evaporation and dry to obtain an iron-molybdenum catalyst, which is recorded as comparative catalyst #1 and set aside.

[0068] The catalyst of comparison 1# was pressed into tablets with a mesh size of 20-60 and then added into the fixed bed reactor. Atmospheric pressure air was introduced at a volume space velocity of 2000 h -1 , raise the temperature to 200 ℃, keep warm for 1 hour, start feeding methanol liquid phase at a flow rate of 20 ml / min, and after 2 hours of reaction, analyze and measure the formaldehyde and methanol solution in the receiving bottle according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution". The methanol conversion rate is 40.7% and the formaldehyde selectivity is 58.6%.

[0069] Comparative Example 2 (i) Add 10.0 g of CeO2 to 50 ml of deionized water, raise the temperature to 60 °C, keep stirring for 2 h, then cool to 40 °C to obtain a mixture; (ii) Add 0.871 g of FeCl3 and 1.839 g of (NH4)2MoO4, keep warm and stir for 4 hours, then remove excess water by rotary evaporation and dry to obtain an iron-molybdenum catalyst, which is recorded as comparative catalyst #2 and set aside.

[0070] The obtained comparative 2# catalyst was pressed into tablets with a size of 20-60 mesh, and then added into a fixed bed reactor and introduced into atmospheric pressure air with a volume space velocity of 2000 h -1 , raise the temperature to 200 ℃, keep warm for 1 hour, start feeding methanol liquid phase at a flow rate of 20 ml / min, and after 2 hours of reaction, analyze and measure the formaldehyde and methanol solution in the receiving bottle according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution". The methanol conversion rate is 45.6% and the formaldehyde selectivity is 48.2%.

[0071] Embodiment 44 Catalyst stability test: The obtained 1# catalyst was pressed into tablets with a size of 20-60 mesh, and then added into a fixed bed reactor and introduced into atmospheric pressure air with a volumetric space velocity of 2000 h -1 , raise the temperature to 200 ℃, keep warm for 1 hour, start feeding methanol liquid phase, the flow rate is 20 ml / min, the formaldehyde and methanol solution in the receiving bottle are analyzed and measured according to the national standard GB / T 9009-2011 "Industrial Formaldehyde Solution". After 300 hours, the conversion rate of methanol is 65.3%, and the selectivity of formaldehyde is 98.5%.

[0072] The present application provides an iron-molybdenum catalyst, which is prepared by the following method: dispersing an organic phosphoric acid modifier into water in a reaction container, adding a carrier and stirring to obtain a mixture; adding an iron source and a molybdenum source to the mixture and mixing; stirring at a constant temperature, removing excess solvent, and drying to obtain an iron-molybdenum catalyst; and providing its application in synthesizing formaldehyde. Compared with the prior art, the present application has the following beneficial effects: 1. The novel iron-molybdenum catalyst provided by the present application is prepared by an impregnation method, and the preparation method is simple. The catalyst includes an active metal, an organic phosphoric acid modifier and a carrier; the organic phosphoric acid modifier is uniformly covered on the catalyst surface, and is coordinated with the active metal ions. 1. The formation of a complex by the reaction of two or more bonds not only improves the activity of the catalyst, but also effectively reduces the loss of active components during the reaction, so that the catalyst obtains high activity and high stability; 2. The reaction temperature of the system is lowered in the formaldehyde synthesis, and the highly selective conversion of methanol to formaldehyde is achieved under relatively mild conditions, the side reactions at high temperatures are suppressed, and the reaction selectivity and yield are improved; In summary, the technical solution of the present application has a moderate reaction temperature, few side reactions, and the catalyst maintains high strength, high activity and high stability, avoiding the phenomenon of bed blockage caused by catalyst pulverization, making the catalyst less likely to deactivate, reducing production costs, improving production efficiency, and facilitating large-scale production.

[0073] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0074] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An iron-molybdenum catalyst, characterized in that Prepared by the following method: (i) dispersing an organophosphoric acid modifier into water in a reaction container, adding a carrier and stirring to obtain a mixture; (ii) adding an iron source and a molybdenum source to the mixture and mixing; stirring while keeping warm, removing excess solvent, and drying to obtain an iron-molybdenum catalyst.

2. An iron-molybdenum catalyst according to claim 1, characterized in that: The organic phosphoric acid modifier in step (i) is one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, aminomethylphosphonic acid, hydroxymethylphosphonic acid, and iminodimethylenephosphonic acid.

3. An iron-molybdenum catalyst according to claim 1, characterized in that: The carrier in step (i) is one or more of zinc oxide, cerium oxide, silicon dioxide, zirconium dioxide and aluminum oxide.

4. An iron-molybdenum catalyst according to claim 1, characterized in that: In step (i), the mass ratio of the organophosphate modifier to the carrier is 0.1-1:

1.

5. An iron-molybdenum catalyst according to claim 1, characterized in that: In step (i), the temperature of the reaction container is 40-80°C, and the stirring time is 1-3 h.

6. An iron-molybdenum catalyst according to claim 1, characterized in that: The iron source in step (ii) is one or more of ferric chloride hexahydrate, ferric nitrate, ferrous sulfate, ferric chloride, ferrous chloride, ferric nitrate nonahydrate, ferrous sulfate heptahydrate, ammonium ferric sulfate dodecahydrate, ferric sulfate or ferric triacetylacetonate; the molybdenum source is one or more of ammonium molybdate, ammonium tetramolybdate, ammonium heptamolybdate, sodium molybdate, sodium molybdate dihydrate, molybdenum acetylacetonate or sodium phosphomolybdate.

7. An iron-molybdenum catalyst according to claim 1, characterized in that: The mass ratio of the iron source to the carrier is 0.01-0.05:1, and the mass ratio of the iron source to the molybdenum source in step (ii) is 1:1-5.

8. An iron-molybdenum catalyst according to claim 1, characterized in that: The temperature of the heat preservation and stirring in step (ii) is 40-60°C and the time is 2-6 hours.

9. An application of an iron-molybdenum catalyst in the preparation of formaldehyde, characterized in that: The iron-molybdenum catalyst according to any one of claims 1 to 8 is added into a fixed bed reactor, gas is introduced, and formaldehyde is prepared by oxidation reaction using methanol as a raw material.

10. Use of an iron-molybdenum catalyst in preparing formaldehyde according to claim 9, characterized in that: The gas is air, the air pressure is normal pressure, and the volume space velocity of the gas is 1000-3000 h -1 ; The reaction temperature is 200-300°C; the methanol feed rate is 10-30 ml / min.

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