An iron-molybdenum catalyst and its application in the preparation of formaldehyde

Abstract

The present application discloses an iron-molybdenum catalyst and its application in the preparation of formaldehyde, which belongs to the field of chemical engineering technology. The present application provides an iron-molybdenum catalyst, which comprises an active metal, an organic phosphoric acid modifier and a carrier, and also provides its application in the synthesis of formaldehyde. This method has a moderate reaction temperature and few side reactions. The catalyst maintains high strength, high activity and high stability, avoids the phenomenon of bed plugging caused by catalyst pulverization, makes the catalyst not easily deactivated, reduces the production cost, improves the production efficiency of formaldehyde, and is conducive to large-scale production.

Description

Technical Field

[0001] This application belongs to the field of chemical engineering technology, and particularly 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 engineering, materials, and medicine. According to a research survey of the global market, the output of formaldehyde in 2020 was 45.6 metric tons, and it is expected to further increase at a rate of 4.65% per year during the period of 2021 - 2028, reaching a market value of 37.7 billion US dollars by 2028. At the same time, China has become the world's largest producer and consumer of formaldehyde, with the production capacity accounting for 55% of the global total production capacity and the consumption accounting for 53%. In the existing domestic formaldehyde production processes, the methanol oxidation process is mainly used, which is divided into the "silver method" and the "iron-molybdenum method" according to different types of catalysts used. The silver catalyst method has a long history. Its advantages are mature process, shorter process flow, lower power consumption, less investment, and large single-series production capacity; its disadvantages are higher methanol consumption, shorter catalyst life, and poor activity.

[0003] Compared with the "silver method", the "iron-molybdenum method" has the advantages of lower reaction temperature, lower methanol unit consumption, longer catalyst service life, and can produce high-concentration formaldehyde solution. However, the iron-molybdenum catalyst method cannot be equipped with a methanol recovery tower, and a large amount of air is required 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 the equipment investment and resulting in poor economic benefits. In addition, the iron-molybdenum catalyst used belongs to one of the most difficult catalysts to prepare, and the catalysts used in the domestic iron-molybdenum process still rely heavily on foreign imports, which causes inconvenience and restrictions to the further application of the iron-molybdenum process for formaldehyde production in China.

[0004] However, the traditional silver method catalyst has the disadvantages of short service life, easy poisoning and inactivation, raw materials need to be pretreated, 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 occurs on the catalyst surface. When methanol reacts with the oxygen on the catalyst surface, formaldehyde is generated and leaves the catalyst surface, and the oxygen entering the reaction system replenishes the catalyst surface to re-form an active catalyst. During the process operation, if the oxygen content in the system is lower than 4.5%, the metal catalyst in the oxidized state will be reduced, and the catalyst activity will be irreversibly reduced, resulting in low methanol conversion and low formaldehyde yield during the later operation.

[0005] Therefore, it is particularly important to seek new process methods and new catalytic technologies for formaldehyde synthesis to improve the 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 this application is to provide an iron-molybdenum catalyst and its application in the preparation of formaldehyde to solve the technical problems existing in the prior art, such as the difficulty in preparing iron-molybdenum catalysts, the instability of catalysts, and the low catalytic efficiency.

[0007] To achieve the above purpose, the technical solution adopted in this application is: to provide an iron-molybdenum catalyst, which is prepared by the following method:

[0008] (1) Disperse the organic phosphoric acid modifier in water in a reaction vessel, add the carrier and stir to obtain a mixture;

[0009] (2) Add an iron source and a molybdenum source to the mixture and mix them; keep warm and stir, remove the excess solvent, and dry to obtain the iron-molybdenum catalyst.

[0010] In one embodiment,

[0011] In step (1), the organic phosphoric acid modifier 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), iminodimethylenephosphonic acid (IDMP, CAS: 17261-34-6).

[0012] In one embodiment,

[0013] In step (1), the carrier is one or more of zinc oxide (ZnO), cerium oxide (CeO2), silicon dioxide (SiO2), zirconium dioxide (ZrO2), and alumina (Al2O3).

[0014] In one embodiment,

[0015] In step (1), the mass ratio of the organic phosphoric acid modifier to the carrier is 0.1-1:1.

[0016] In one embodiment,

[0017] In step (1), the temperature of the reaction vessel is 40-80 °C, and the stirring time is 1-3 h.

[0018] In one embodiment,

[0019] Step (ii): The iron source is selected from one or more of iron-containing hydrochlorides, sulfates, nitrates, acetylacetonates, and their hydrates; more specifically, the iron source is 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 iron(III) sulfate dodecahydrate (NH4Fe(SO4)2·12H2O), ferric sulfate (Fe2(SO4)3), or iron(III) acetylacetonate (Fe(acac)3); the molybdenum source is selected from one or more of ammonium molybdate, sodium molybdate, molybdenum acetylacetonate, sodium molybdate dihydrate, and sodium dodecaphosphomolybdate hydrate; 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).

[0020] In one embodiment,

[0021] 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.

[0022] In one embodiment,

[0023] The temperature for heat preservation and stirring in step (ii) is 40 - 60 °C, and the time is 2 - 6 h.

[0024] This application also provides an application of an iron-molybdenum catalyst in the preparation of formaldehyde. Using the iron-molybdenum catalyst of any of the above embodiments, the iron-molybdenum catalyst is added to a fixed-bed reactor, and a gas is introduced to oxidize methanol as a raw material to prepare formaldehyde.

[0025] In one embodiment,

[0026] 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 , which is appropriate to meet the reaction requirements and is not limited here; the reaction temperature is 200 - 300 °C; the feed rate of methanol is 10 - 30 ml / min.

[0027] The present application provides an iron-molybdenum catalyst and its application in the synthesis of 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 uniformly covers the surface of the catalyst and forms a complex with the active metal ions through coordination bonds, which not only improves the activity of the catalyst but also effectively reduces the loss of active components during the reaction process, enabling the catalyst to obtain high activity and high stability; 2. In the synthesis of formaldehyde, the reaction temperature of the system is reduced, and the high-selectivity conversion of methanol to formaldehyde is achieved under relatively mild conditions, suppressing side reactions at high temperatures and improving the reaction selectivity and yield; In summary, the technical solution of the present application has a moderate reaction temperature and few side reactions. The catalyst maintains high strength, high activity, and high stability, avoiding the phenomenon of bed plugging caused by catalyst pulverization, making the catalyst not easily deactivated, reducing production costs, and improving production efficiency, which is beneficial to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 An electron microscope photograph of the iron-molybdenum catalyst magnified 50 times;

[0030] Figure 2 An electron microscope photograph of the iron-molybdenum catalyst magnified 200 times. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to make the technical problems to be solved, technical solutions, and beneficial effects of the present application clearer and more understandable, the present application will be 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.

[0032] After the reaction is completed, the reaction solution in the receiving flask is collected, and formaldehyde is analyzed and measured according to the national standard GB / T 9009-2011 "Formaldehyde Solution for Industrial Use".

[0033]

[0034]

[0035] Example 1

[0036] (1) Add 50 ml of deionized water and 7.0 g of DTPMP to the reaction vessel, then add 10.0 g of CeO2. Raise the temperature to 60 °C, stir for 2 h while maintaining the temperature, and then cool down to 40 °C to obtain a mixture.

[0037] (2) Add 1.452 g of FeCl3·6H2O and 1.839 g of (NH4)2MoO4 to the mixture. Stir at 40 °C for 4 h while maintaining the temperature, then rotary evaporate to remove the excess water, and dry to obtain an iron-molybdenum catalyst, denoted as Catalyst 1#, for standby. The structural characterization is as Figure 1-2 shown. Instrument model: JEOL JSM-6701F;

[0038] Press the Catalyst 1# into tablets with a particle size of 20 - 60 mesh, then add it to the fixed-bed reactor. Introduce atmospheric air with a space velocity of 2000 h -1 . Raise the temperature to 200 °C, maintain the temperature for 1 h, then start the liquid-phase feeding of methanol at a flow rate of 20 ml / min. After reacting for 2 h, for the formaldehyde and methanol solution in the receiving flask, analyze and measure it according to the national standard GB / T 9009-2011 "Formaldehyde Solution for Industrial Use". The methanol conversion rate is 63.4%, and the formaldehyde selectivity is 98.7%.

[0039] Example 2

[0040] The difference between this example and Example 1 is that after adding the Catalyst 1# to the fixed-bed reactor, raise the temperature to 300 °C, and the other operations are the same. The methanol conversion rate is 65.8%, and the formaldehyde selectivity is 96.2%.

[0041] Example 3

[0042] The difference between this example and Example 1 is that the liquid-phase feeding rate of methanol 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%.

[0043] Example 4

[0044] The difference between this example and Example 1 is that the liquid-phase feeding rate of methanol 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%.

[0045] Example 5

[0046] The difference between this example and Example 1 is that in step (2), replace FeCl3·6H2O with 2.59 g of NH4Fe(SO4)2·12H2O to obtain Catalyst 2#, and the other operations are the same. The methanol conversion rate is 63.8%, and the formaldehyde selectivity is 98.1%.

[0047] Example 6

[0048] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 1.493 g of FeSO4·7H2O to prepare catalyst No. 3, and the remaining operations were the same. The methanol conversion rate was 63.2%, and the formaldehyde selectivity was 98.3%.

[0049] Example 7

[0050] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 2.148 g of Fe2(SO4)3 to prepare catalyst No. 4, and the remaining operations were the same. The methanol conversion rate was 63.0%, and the formaldehyde selectivity was 98.4%.

[0051] Example 8

[0052] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 0.871 g of FeCl3 to prepare catalyst No. 5, and the remaining operations were the same. The methanol conversion rate was 63.5%, and the formaldehyde selectivity was 98.7%.

[0053] Example 9

[0054] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 2.170 g of Fe(NO3)3·9H2O to prepare catalyst No. 6, and the remaining operations were the same. The methanol conversion rate was 62.8%, and the formaldehyde selectivity was 98.2%.

[0055] Example 10

[0056] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 0.681 g of FeCl2 to prepare catalyst No. 7, and the remaining operations were the same. The methanol conversion rate was 62.8%, and the formaldehyde selectivity was 98.2%.

[0057] Example 11

[0058] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O was replaced with 1.897 g of Fe(acac)3 to prepare catalyst No. 8, and the remaining operations were the same. The methanol conversion rate was 62.5%, and the formaldehyde selectivity was 98.3%.

[0059] Example 12

[0060] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 6.228 g of (NH4)2Mo4O 13·2H2O was used to prepare Catalyst 9. With the same operations for the rest, the methanol conversion rate was 65.1% and the formaldehyde selectivity was 97.8%.

[0061] Example 13

[0062] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 11.593 g of (NH4)6Mo7O 24 ·4H2O was used to prepare Catalyst 10. With the same operations for the rest, the methanol conversion rate was 63.4% and the formaldehyde selectivity was 98.1%.

[0063] Example 14

[0064] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 1.932 g of Na2MoO4 to prepare Catalyst 11. With the same operations for the rest, the methanol conversion rate was 64.2% and the formaldehyde selectivity was 98.4%.

[0065] Example 15

[0066] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 2.270 g of Na2MoO4·2H2O to prepare Catalyst 12. With the same operations for the rest, the methanol conversion rate was 63.2% and the formaldehyde selectivity was 98.3%.

[0067] Example 16

[0068] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 3.060 g of MoO6(acac)2 to prepare Catalyst 13. With the same operations for the rest, the methanol conversion rate was 63.6% and the formaldehyde selectivity was 97.6%.

[0069] Example 17

[0070] The difference between this example and Example 8 is that in step (ii), (NH4)2MoO4 was replaced with 17.741 g of Na3PO4·12MoO3 to prepare Catalyst 14. With the same operations for the rest, the methanol conversion rate was 63.4% and the formaldehyde selectivity was 97.2%.

[0071] Example 18

[0072] The difference between this example and Example 8 is that in step (i), CeO2 was replaced with ZnO to prepare Catalyst 15. With the same operations for the rest, the methanol conversion rate was 60.7% and the formaldehyde selectivity was 97.5%.

[0073] Example 19

[0074] The difference between this example and Example 8 is that in step (i), CeO2 is replaced with SiO2 to prepare the 16# catalyst, and the remaining operations are the same. The methanol conversion rate is 61.2%, and the formaldehyde selectivity is 97.1%.

[0075] Example 20

[0076] The difference between this example and Example 8 is that in step (i), CeO2 is replaced with ZrO2 to prepare the 17# catalyst, and the remaining operations are the same. The methanol conversion rate is 60.7%, and the formaldehyde selectivity is 97.6%.

[0077] Example 21

[0078] The difference between this example and Example 8 is that in step (i), CeO2 is replaced with Al2O3 to prepare the 18# catalyst, and the remaining operations are the same. The methanol conversion rate is 62.5%, and the formaldehyde selectivity is 97.4%.

[0079] Example 22

[0080] The difference between this example and Example 8 is that in step (i), DTPMP is replaced with NTMP to prepare the 19# catalyst, and the remaining operations are the same. The methanol conversion rate is 62.8%, and the formaldehyde selectivity is 97.8%.

[0081] Example 23

[0082] The difference between this example and Example 8 is that in step (i), DTPMP is replaced with EDTMP to prepare the 20# catalyst, and the remaining operations are the same. The methanol conversion rate is 63.1%, and the formaldehyde selectivity is 98.5%.

[0083] Example 24

[0084] The difference between this example and Example 8 is that in step (i), DTPMP is replaced with AMP to prepare the 21# catalyst, and the remaining operations are the same. The methanol conversion rate is 63.0%, and the formaldehyde selectivity is 98.0%.

[0085] Example 25

[0086] The difference between this example and Example 8 is that in step (i), DTPMP is replaced with IDMP to prepare the 22# catalyst, and the remaining operations are the same. The methanol conversion rate is 63.2%, and the formaldehyde selectivity is 98.1%.

[0087] Example 26

[0088] The difference between this example and Example 8 is that in step (i), DTPMP is replaced with 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%.

[0089] Example 27

[0090] The difference between this example and Example 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%.

[0091] Example 28

[0092] The difference between this example and Example 8 is that in step (i), after adding CeO2, the temperature is raised to 80 °C to obtain Catalyst 25#, and the remaining operations are the same. The methanol conversion rate is 65.4%, and the formaldehyde selectivity is 97.1%.

[0093] Example 29

[0094] The difference between this example and Example 8 is that in step (i), after heating, the mixture is kept warm and stirred for 1 h to obtain Catalyst 26#, and the remaining operations are the same. The methanol conversion rate is 59.4%, and the formaldehyde selectivity is 98.0%.

[0095] Example 30

[0096] The difference between this example and Example 8 is that in step (i), after heating, the mixture is kept warm and stirred for 3 h to obtain Catalyst 27#, and the remaining operations are the same. The methanol conversion rate is 64.3%, and the formaldehyde selectivity is 98.2%.

[0097] Example 31

[0098] The difference between this example and Example 8 is that in step (i), after keeping warm and stirring for 2 h, the temperature is lowered to 50 °C to obtain Catalyst 28#, and the remaining operations are the same. The methanol conversion rate is 62.1%, and the formaldehyde selectivity is 97.0%.

[0099] Example 32

[0100] The difference between this example and Example 8 is that in step (i), after keeping warm and stirring for 2 h, no temperature reduction treatment is performed to obtain Catalyst 29#, and the remaining operations are the same. The methanol conversion rate is 61.3%, and the formaldehyde selectivity is 96.4%.

[0101] Example 33

[0102] In this example, different from Example 8, in step (ii), stir at 50 °C for 2 h to obtain Catalyst 30, and the remaining operations are the same. The methanol conversion rate is 61.2%, and the formaldehyde selectivity is 97.0%.

[0103] Example 34

[0104] In this example, different from Example 8, in step (ii), stir at 60 °C for 6 h to obtain Catalyst 31, and the remaining operations are the same. The methanol conversion rate is 65.7%, and the formaldehyde selectivity is 98.4%.

[0105] Example 35

[0106] In this example, different from Example 8, in step (ii), the mass of (NH4)2MoO4 is 0.613 g to obtain Catalyst 32, and the remaining operations are the same. The methanol conversion rate is 63.1%, and the formaldehyde selectivity is 98.1%.

[0107] Example 36

[0108] In this example, different from Example 8, in step (ii), the mass of (NH4)2MoO4 is 3.065 g to obtain Catalyst 33, and the remaining operations are the same. The methanol conversion rate is 64.7%, and the formaldehyde selectivity is 99.0%.

[0109] Example 37

[0110] In this example, different from Example 8, in step (i), the mass of DTPMP is 1.0 g to obtain Catalyst 34, and the remaining operations are the same. The methanol conversion rate is 60.0%, and the formaldehyde selectivity is 96.4%.

[0111] Example 38

[0112] In this example, different from Example 8, in step (i), the mass of DTPMP is 5.0 g to obtain Catalyst 35, and the remaining operations are the same. The methanol conversion rate is 61.2%, and the formaldehyde selectivity is 97.8%.

[0113] Example 39

[0114] In this example, different from Example 8, in step (i), the mass of DTPMP is 10.0 g to obtain Catalyst 36, and the remaining operations are the same. The methanol conversion rate is 65.8%, and the formaldehyde selectivity is 98.9%.

[0115] Example 40

[0116] The difference between this example and Example 8 is that in step (ii), the mass of FeCl3 is 0.29 g, the mass of (NH4)2MoO4 is 0.613 g, and catalyst 37# is prepared. The remaining operations are the same. The methanol conversion rate is 60.7%, and the formaldehyde selectivity is 97.3%.

[0117] Example 41

[0118] The difference between this example and Example 8 is that in step (ii), the mass of FeCl3 is 1.452 g, the mass of (NH4)2MoO4 is 3.065 g, and catalyst 38# is prepared. The remaining operations are the same. The methanol conversion rate is 66.2%, and the formaldehyde selectivity is 98.5%.

[0119] Example 42

[0120] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O is replaced with 0.816 g of FeSO4, and catalyst 39# is prepared. The remaining operations are the same. The methanol conversion rate is 63.2%, and the formaldehyde selectivity is 98.3%.

[0121] Example 43

[0122] The difference between this example and Example 1 is that in step (ii), FeCl3·6H2O is replaced with 1.299 g of Fe2(NO3)3, and catalyst 40# is prepared. The remaining operations are the same. The methanol conversion rate is 62.7%, and the formaldehyde selectivity is 98.2%.

[0123] Comparative Example 1

[0124] (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, and then cool down to 40 °C to obtain a mixture.

[0125] (ii). Add 0.871 g of FeCl3, keep stirring for 4 h, then rotary evaporate to remove the excess water and dry to obtain an iron-molybdenum catalyst, denoted as comparative catalyst 1#, for standby.

[0126] Press the comparative catalyst 1# into tablets with a size of 20 - 60 mesh, then add it to a fixed-bed reactor, introduce normal-pressure air, with a volumetric space velocity of 2000 h -1 , raise the temperature to 200 °C, keep it warm for 1 h, then start the liquid-phase methanol feeding with a flow rate of 20 ml / min. After reacting for 2 h, for the formaldehyde and methanol solution in the receiving flask, analyze and measure it according to the national standard GB / T 9009 - 2011 "Formaldehyde Solution for Industrial Use". The methanol conversion rate is 40.7%, and the formaldehyde selectivity is 58.6%.

[0127] Comparative Example 2

[0128] (1) Add 10.0 g of CeO2 to 50 ml of deionized water, raise the temperature to 60 °C, keep stirring for 2 h, and then cool down to 40 °C to obtain a mixture;

[0129] (2) Add 0.871 g of FeCl3 and 1.839 g of (NH4)2MoO4, keep stirring for 4 h, then rotary evaporate to remove the excess water and dry to obtain an iron-molybdenum catalyst, denoted as Comparative 2# catalyst, for standby.

[0130] Press the obtained Comparative 2# catalyst into tablets of 20 - 60 mesh, then add it into a fixed-bed reactor, introduce atmospheric air, with a volumetric space velocity of 2000 h -1 , raise the temperature to 200 °C, keep it for 1 h, then start the liquid-phase feeding of methanol with a flow rate of 20 ml / min. After reacting for 2 h, for the formaldehyde and methanol solution in the receiving flask, analyze and measure it according to the national standard GB / T 9009-2011 "Formaldehyde Solution for Industrial Use". The methanol conversion rate is 45.6%, and the formaldehyde selectivity is 48.2%.

[0131] Example 44

[0132] Catalyst stability experiment: Press the obtained 1# catalyst into tablets of 20 - 60 mesh, then add it into a fixed-bed reactor, introduce atmospheric air, with a volumetric space velocity of 2000 h -1 , raise the temperature to 200 °C, keep it for 1 h, then start the liquid-phase feeding of methanol with a flow rate of 20 ml / min. For the formaldehyde and methanol solution in the receiving flask, analyze and measure it according to the national standard GB / T 9009-2011 "Formaldehyde Solution for Industrial Use". After 300 h, the methanol conversion rate is 65.3%, and the formaldehyde selectivity is 98.5%.

[0133] The present application provides an iron-molybdenum catalyst, which is prepared by the following method: dispersing an organic phosphoric acid modifier in water in a reaction vessel, adding a carrier and stirring to obtain a mixture; adding an iron source and a molybdenum source to the mixture and mixing; keeping warm and stirring, removing excess solvent, and drying to obtain the iron-molybdenum catalyst; and provides its application in the synthesis of 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 the 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 uniformly covers the surface of the catalyst and forms a complex with the active metal ions through coordination bonds, which not only improves the activity of the catalyst, but also effectively reduces the loss of active components during the reaction process, so that the catalyst obtains high activity and high stability; 2. In the synthesis of formaldehyde, the reaction temperature of the system is reduced, and the high-selectivity conversion of methanol to formaldehyde is realized under relatively mild conditions, the side reactions at high temperature are inhibited, and the reaction selectivity and yield are improved; In summary, the technical solution of the present application has a moderate reaction temperature and few side reactions, the catalyst maintains high strength, high activity and high stability, avoids the phenomenon of bed plugging caused by catalyst pulverization, makes the catalyst not easily deactivated, reduces the production cost, improves the production efficiency, and is beneficial to large-scale production.

[0134] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0135] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An iron-molybdenum catalyst, characterized in that, Prepared by the following method: (1) Disperse the organic phosphonic acid modifier in water in a reaction vessel, add the carrier and stir to obtain a mixture; (2) Add an iron source and a molybdenum source to the mixture and mix them; keep warm and stir, remove the excess solvent, and dry to obtain an iron-molybdenum catalyst; The organic phosphonic acid modifier in step (1) is one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, aminomethylphosphonic acid, hydroxymethylphosphonic acid, and iminodimethylenephosphonic acid.

2. The iron-molybdenum catalyst according to claim 1, characterized in that, The carrier in step (1) is one or more of zinc oxide, cerium oxide, silica, zirconia, and alumina.

3. The iron-molybdenum catalyst according to claim 1, wherein, The mass ratio of the organic phosphonic acid modifier to the carrier in step (1) is 0.1-1:

1.

4. A ferromolybdenum catalyst according to claim 1, characterized in that, The temperature of the reaction vessel in step (1) is 40-80 °C, and the stirring time is 1-3 h.

5. A ferromolybdenum catalyst according to claim 1, wherein, The iron source in step (2) is one or more of iron nitrate, ferrous sulfate, ferric chloride, ferrous chloride, ammonium ferric sulfate dodecahydrate, ferric sulfate, or iron(III) acetylacetonate; the molybdenum source is one or more of ammonium molybdate, ammonium tetramolybdate, ammonium heptamolybdate, sodium molybdate, molybdenum(VI) acetylacetonate, or sodium phosphomolybdate.

6. The 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 (2) is 1:1-5.

7. A ferromolybdenum catalyst according to claim 1, characterized in that, The temperature of the heat preservation and stirring in step (2) is 40-60 °C, and the time is 2-6 h.

8. Use of an iron-molybdenum catalyst in the preparation of formaldehyde, characterized in that, Using the iron-molybdenum catalyst according to any one of claims 1-7, add the iron-molybdenum catalyst to a fixed-bed reactor, introduce a gas, and oxidize methanol as a raw material to prepare formaldehyde.

9. Use of an iron-molybdenum catalyst according to claim 8 in the preparation of formaldehyde, 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 temperature of the reaction is 200 - 300 °C; the feed rate of methanol is 10 - 30 ml / min.

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