CN113368863A - Preparation method of eggshell type iron-molybdenum catalyst containing silicon dioxide - Google Patents

Preparation method of eggshell type iron-molybdenum catalyst containing silicon dioxide Download PDF

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CN113368863A
CN113368863A CN202110739966.7A CN202110739966A CN113368863A CN 113368863 A CN113368863 A CN 113368863A CN 202110739966 A CN202110739966 A CN 202110739966A CN 113368863 A CN113368863 A CN 113368863A
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silicon dioxide
molybdenum
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eggshell
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曲俊嬴
周焕文
邓少亮
乔川
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Dalian Ruike Technology Co ltd
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    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
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    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/396—Distribution of the active metal ingredient
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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Abstract

A preparation method of an eggshell type iron-molybdenum catalyst containing silicon dioxide, belonging to the technical field of catalysts. The method is characterized in that soluble ferric salt and soluble molybdenum salt are coprecipitated under certain conditions, are aged, washed, dried and crushed into small particles, are roasted, are combined with silicon dioxide, and allow the silicon dioxide to wrap micron-sized active particles to form an eggshell-shaped structure with the active component small particles as an inner core and the silicon oxide as an outer shell, and are tabletted and molded after roasting to obtain a catalyst finished product. The method can effectively disperse the active center of the catalyst, provides more and wider pore channels for the adsorption and desorption of reactants on the catalyst, thereby improving the activity of the catalyst, effectively dispersing the heat on the surface of the catalyst and reducing the loss of molybdenum caused by local high temperature. Meanwhile, the mechanical strength of the catalyst is well improved by adding a proper amount of silicon dioxide. The catalyst prepared by the method has high activity, few byproducts, good mechanical strength and longer service life.

Description

Preparation method of eggshell type iron-molybdenum catalyst containing silicon dioxide
Technical Field
The invention belongs to the field of organic chemical catalysts, and particularly relates to a preparation method of a catalyst for preparing formaldehyde by oxidizing iron-molybdenum methanol with a silica eggshell type structure.
Background
Formaldehyde is an important basic organic chemical raw material and is widely used in chemical industry, medicine, textile, wood processing and petroleum industry. The modern industrial formaldehyde production mainly adopts a methanol oxidation method. The iron-molybdenum formaldehyde catalyst has wide application due to the advantages of the iron-molybdenum formaldehyde catalyst in performance. With the pulling of new industries such as polyformaldehyde engineering plastics and the like and the improvement of the requirements of national environmental protection laws and regulations, the iron-molybdenum process is bound to be developed in China.
There are many patents for preparing formaldehyde catalyst by methanol oxidation at home and abroad, such as US4829042, CN1100667A, CN1546232A, CN102240554B, etc. Although the methods can prepare the catalyst with high activity, the methods cannot better solve the problems of catalyst deactivation and short service life caused by the loss of the active component molybdenum due to high surface temperature in the using process of the catalyst. The average life of current commercial iron-molybdenum catalysts is 6-12 months and many catalysts lose activity soon after they are put into service. The accompanying phenomena are that the activity of the catalyst is reduced, the selectivity is reduced, and the resistance of a catalyst bed layer is increased. The main reasons for deactivation are sublimation loss of molybdenum, phase decomposition, catalyst pulverization, thermal sintering, etc. Wherein molybdenum sublimation loss is a major cause of deactivation of the iron-molybdenum catalyst. And the loss of molybdenum is mostly generated on the surface of the catalyst, and iron oxide is easily formed on the surface of the catalyst after the molybdenum is sublimated, so that the selectivity is reduced. Meanwhile, as the main active components of the catalyst are molybdenum oxide and iron molybdate, the loss of molybdenum can cause the reduction of activity and collapse and pulverization of the catalyst.
Disclosure of Invention
The invention aims to provide a preparation method of a catalyst containing silicon dioxide and having an eggshell-type structure for preparing formaldehyde by oxidizing methanol with an iron-molybdenum method. The catalyst is characterized in that micron-sized particles of an active component are wrapped into an eggshell-shaped structure by silicon dioxide. The catalyst has high activity and selectivity, good mechanical strength and long service life. The eggshell structure enables the active component to be wrapped, the active component has high dispersity, the catalyst has good mechanical strength and good selectivity, and the local overtemperature phenomenon caused by burning explosion of the surface of the catalyst is effectively prevented, so that the loss of molybdenum is relieved, the activity of the catalyst is improved, and the service life of the catalyst is prolonged.
The catalyst is prepared by coprecipitating soluble ferric salt and soluble molybdenum salt with certain concentration under certain conditions, aging, washing, drying, crushing into 50-250 micron particles, roasting to obtain a precursor of the catalyst, combining with silicon dioxide, roasting and molding.
Mo of the catalyst: fe = 1.5-4, coprecipitating for 0.5-3h at 40-100 ℃, controlling the pH value of the coprecipitation to be 1.0-2.0 by ammonia water, reacting under stirring, wherein the aging temperature is 40-100 ℃, and the aging time is 3-15 h. Washing with deionized water. Drying the synthesized catalyst, and crushing the catalyst into particles of 50-250 microns. The pulverization method is not limited to a specific one, and pulverization by a pulverizer, ball milling, or jet milling may be used. Calcining at the temperature of 420-600 ℃ to obtain the precursor of the catalyst.
The structure of the silica shell wrapping micron-sized active components can be realized by putting micron-sized particles of the catalyst active components into a sugar coating machine, and adding the silica in a liquid spraying coating mode after the machine is operated. The structure may also be formed by dipping. The added silicon source is preferably nano-scale silicon dioxide, such as silica sol and gas-phase hydrophilic white carbon black, and the adding amount of the silicon dioxide is 20-30wt% of the active components of the catalyst. The manner of coating the silica shell with the catalyst active component is not limited to one, and liquid spray coating, impregnation and other manners can be adopted. The material is calcined at the temperature of 420-500 ℃ after being dried, and finally the catalyst is made into a hollow cylinder with phi 4.5 multiplied by 1.3 multiplied by 4.5mm (outer diameter multiplied by wall thickness multiplied by height), thus obtaining the catalyst finished product.
The invention has the beneficial effects that: the method has the advantages that a proper amount of silicon dioxide and micron-sized active component small particles of the catalyst are added to form an eggshell type structure, so that the active components can be better dispersed, deflagration caused by local high temperature due to active component aggregation on the surface of the catalyst can be effectively prevented, the temperature of hot spots is remarkably reduced, and the rapid loss of molybdenum oxide caused by high temperature on the surface of the catalyst can be effectively controlled. After the catalyst is subjected to heat resistance for 50 hours at the temperature of 380 ℃, the catalytic performance of the catalyst is equivalent to that before the heat resistance, and the catalyst has good heat resistance.
Meanwhile, the addition of the silicon dioxide can enable the active components of the catalyst to form a plurality of independent individuals, prevent the hardening of the active components of the catalyst in the forming process, increase pore spaces of the catalyst, and be more beneficial to the adsorption and desorption of reactants on the catalyst, thereby improving the activity of the catalyst. The catalyst was run on a pilot plant with the formaldehyde yield essentially maintained at around 94%.
The addition of a proper amount of silica has the advantages of increasing the mechanical strength of the catalyst and preventing bed layer blockage caused by pulverization of the catalyst during use. The catalyst is heated for 50 hours at the temperature of 380 ℃ and then is subjected to catalytic reaction, and the catalyst still has good strength and basically has no pulverization phenomenon from the viewpoint of evaluation of the discharged catalyst.
Therefore, the addition of a proper amount of silicon dioxide can effectively reduce the loss of molybdenum on the surface of the catalyst, and can ensure that the catalyst has higher activity while increasing the mechanical strength of the catalyst, thereby leading the catalyst to have longer service life.
Drawings
Fig. 1 is a schematic diagram of a structure of a silica-coated micron-sized active component small particle.
Detailed Description
In order to further explain the present invention in detail, specific examples are given below, but the present invention is not limited to the examples given.
Example 1
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then taking 80.92g of ammonium heptamolybdate, adding deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, coprecipitating under stirring, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into particles with the particle size of 100 microns, roasting at the temperature of 450 ℃/6h under the atmosphere of ventilation to obtain a catalyst active component, placing the catalyst active component in a sugar coating machine, taking 70g of silica sol with the silicon content of 25%, uniformly spraying the silica sol onto the catalyst active component after the machine operates, roasting the material under the atmosphere of ventilation for 500 ℃/2h after the material is dried, making into particles of 4.5 × 1.3 × 4.5mm (outer diameter × wall thickness × height) to obtain the final product.
Example 2
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then taking 80.92g of ammonium heptamolybdate, adding deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, coprecipitating under stirring, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into particles with the particle size of 100 microns, roasting at the temperature of 450 ℃/6h under the atmosphere of ventilation to obtain a catalyst active component, placing the catalyst active component in a sugar coating machine, taking 80g of silica sol with the silicon content of 25%, uniformly spraying the silica sol onto the catalyst active component after the machine operates, roasting the material under the atmosphere of ventilation for 500 ℃/2h after the material is dried, making into particles of 4.5 × 1.3 × 4.5mm (outer diameter × wall thickness × height) to obtain the final product.
Example 3
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then adding 80.92g of ammonium heptamolybdate to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution to molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, stirring and coprecipitating, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into small balls with the particle size of 100 microns, roasting at the temperature of 450 ℃/6h in an air atmosphere to obtain a catalyst active component, soaking the catalyst active component in 70g of silica sol with the silicon content of 25%, uniformly soaking, roasting after drying the material, at the temperature of 500 ℃/2h in the air atmosphere, and tabletting to prepare particles with the particle size of 4.5 x 1.3 x 4.5mm (the outer diameter x the wall thickness x the height), and obtaining a catalyst finished product.
Example 4
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then taking 80.92g of ammonium heptamolybdate, adding deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, stirring and coprecipitating, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into particles with the particle size of 100 microns and 200 microns, roasting at the temperature of 450 ℃/6h in the air atmosphere to obtain a catalyst active component, placing the catalyst active component in a sugar coating machine, taking 20g of white carbon black with low specific surface area, adding 60g of pure water for pulping, uniformly spraying slurry onto the catalyst active component, drying the material, roasting at the temperature of 500 ℃/2h in the air atmosphere, and (3) tabletting to prepare particles with the diameter of 4.5 multiplied by 1.3 multiplied by 4.5mm (the outer diameter multiplied by the wall thickness multiplied by the height) to obtain the finished catalyst.
Example 5 comparative example without silica addition
Adding deionized water into 77.8g of ferric nitrate nonahydrate to prepare a solution with the volume of 750ml, adding 80.92g of ammonium heptamolybdate into deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, stirring and coprecipitating, reacting for 2 hours, aging for 10 hours after dropwise adding, filtering, washing, drying, roasting at the temperature of 450 ℃/6 hours under the atmosphere of air, roasting at the temperature of 500 ℃/2 hours under the atmosphere of air, and tabletting to prepare particles with the diameter of 4.5 multiplied by 1.3 multiplied by 4.5mm (the outer diameter is multiplied by the wall thickness and the height), thereby obtaining the catalyst finished product.
Example 6 comparative example with insufficient silica
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then taking 80.92g of ammonium heptamolybdate, adding deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, coprecipitating under stirring, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into particles with the particle size of 100 microns, roasting at the temperature of 450 ℃/6h under the atmosphere of ventilation to obtain a catalyst active component, placing the catalyst active component in a sugar coating machine, taking 40g of silica sol with the silicon content of 25%, uniformly spraying the silica sol onto the catalyst active component after the machine operates, roasting the material under the atmosphere of ventilation for 500 ℃/2h after the material is dried, and (4) tabletting to obtain particles with the diameter of 4.5 multiplied by 1.3 multiplied by 4.5mm (outer diameter multiplied by wall thickness multiplied by height), and obtaining the finished catalyst.
Example 7 comparative example with excess silica
Taking 77.8g of ferric nitrate nonahydrate, adding deionized water to prepare a solution with the volume of 750ml, then taking 80.92g of ammonium heptamolybdate, adding deionized water to prepare a solution with the volume of 1950ml, adjusting the pH of the ammonium molybdate solution to be =2.0 by 49% of nitric acid, dropwise adding the ferric salt solution into molybdenum salt, reacting at the temperature of 70 ℃, adjusting the pH of the reaction to be =1.5 by 5% of ammonia water, coprecipitating under stirring, reacting for 2h, aging for 10h after dropwise adding, filtering, washing, drying, grinding a catalyst ball into particles with the particle size of 100 microns, roasting at the temperature of 450 ℃/6h under the atmosphere of ventilation to obtain a catalyst active component, placing the catalyst active component in a sugar coating machine, taking 120g of silica sol with the silicon content of 25%, uniformly spraying the silica sol onto the catalyst active component after the machine operates, roasting the material under the atmosphere of ventilation for 500 ℃/2h after the material is dried, making into particles of 4.5 × 1.3 × 4.5mm (outer diameter × wall thickness × height) to obtain the final product.
Example 8 Heat resistance test-Life test
The catalyst obtained in example 1 was heat-resistant at a temperature of 380 ℃ for 50 hours to obtain a catalyst sample.
Example 9 insufficient Heat resistance test of SiO 2-lifetime investigation
The catalyst obtained in example 6 was heat-resistant at a temperature of 380 ℃ for 50 hours to obtain a catalyst sample.
Example 10 excessive Heat resistance test of SiO 2-lifetime investigation
The catalyst obtained in example 7 was heat-resistant at a temperature of 380 ℃ for 50 hours to obtain a catalyst sample.
The catalytic performance evaluation conditions and results of the catalyst are as follows, and the catalyst is filled by adopting a pilot plant of Dalikeelix science and technology GmbH:
the packing height is designed as follows
A lower end socket of the reactor: adopts phi 20 ceramic balls and phi 6 ceramic rings to be mixed and filled
The bottom of the tube array: 15cm ceramic ring (phi 5)
A second layer: 65cm pure catalyst
And a third layer: 65cm mixed layer (volume ratio of catalyst to phi 5 ceramic ring is 1: 1)
The top of the tube array: 15cm ceramic ring (phi 5)
Single tube size of reactor: phi 25 x 21.6 m
In the experiment, 6 tubes are filled, and the pure catalyst accounts for 60.94 percent of the total content.
Process conditions
Space velocity (calculated as pure catalyst): 8500 h-1；
Concentration of methanol in reaction gas: 8.5% voL
Oxygen content of the reaction gas: 10.7% voL
Evaluation results table
Figure 223156DEST_PATH_IMAGE002
Note: the above is pilot plant evaluation data for 10 examples, and example 5 is a catalyst prepared without silica addition, example 6 is a catalyst with insufficient SiO2 addition, and example 7 is a catalyst with excessive SiO2 encapsulation.
Examples 8, 9 and 10 are catalysts obtained by subjecting examples 1, 6 and 7 to heat-resistant treatment at 380 ℃ for 50 hours, respectively.
As can be seen from examples 1 to 4, SiO2The normal amount of the added catalyst basically has the formaldehyde yield of about 94 percent, high yield and few byproducts. In example 8, the performance of the catalyst after heat resistance was still maintained at a high level, and from the evaluation of the catalyst after discharge, the catalyst still had good strength and was substantially free from powdering.
Example 5 is without addingInto SiO2The yield of formaldehyde of the catalyst is 84.9 percent, the yield is low, and the by-product is relatively high. Because the active components of the catalyst are aggregated, reactants cannot be well diffused on the surface of the catalyst, the reaction on the surface of the catalyst is relatively violent, and Fe2O3The exposure results in deep oxidation of the reactants and increased by-products.
Examples 6 and 9 are SiO2The yield of formaldehyde in example 6 is 88%, which is lower than that of the catalyst with insufficient addition amount, but the overall performance is better than that of the catalyst without SiO2Due to SiO2The addition amount is insufficient, the coating effect is not good, and the condition of easy deep oxidation still exists, so that the by-product is relative to SiO2The amount of catalyst added is usually excessive. And the heat resistance is poor, the yield of formaldehyde is reduced from 88% to 80%, and the performance of the catalyst is reduced after heat resistance.
SiO in example 7 and example 102Excessive catalyst is coated excessively, so that the active components cannot fully play a role, the activity of the catalyst is low, the yield of formaldehyde is only about 77%, and the yield is low. And from the observation of the catalyst discharged after evaluation, the catalyst strength was poor and the powdering was severe.

Claims (4)

1. The preparation method of the eggshell type iron-molybdenum catalyst containing silicon dioxide is characterized by comprising the following steps:
the catalyst adopts a structure that the shell of silicon dioxide coats the center of an active component of the catalyst;
(1) the method comprises the following steps of (1) coprecipitating soluble ferric salt and soluble molybdenum salt, wherein the temperature of the coprecipitation is 40-100 ℃, the dripping time is 0.5-3h, the pH value of the coprecipitation is controlled to be 1.0-2.0 by ammonia water, the reaction is carried out under stirring, the aging temperature is 40-100 ℃, and the aging time is 3-15 h; washing with acidified deionized water;
(2) crushing the synthesized catalyst drying material into particles of 50-250 microns;
(3) roasting the crushed particles at the temperature of 420-600 ℃ to obtain an active component of the catalyst;
(4) taking the active component of the catalyst as the center, wrapping the surface of the active center of the catalyst with silicon dioxide by adopting a liquid spraying coating or dipping method, wherein the adding amount of the silicon dioxide is 20-30wt% of the active component of the catalyst;
(5) after the materials are dried, the materials are roasted at the temperature of 420-500 ℃ in the atmosphere of air, and the catalyst is flaked to obtain the finished product of the catalyst.
2. The process for preparing an eggshell iron-molybdenum catalyst containing silica as claimed in claim 1, wherein: the soluble ferric salt is ferric nitrate and the soluble molybdenum salt is ammonium molybdate.
3. The process for preparing an eggshell iron-molybdenum catalyst containing silica as claimed in claim 1, wherein: the crushing method is crushing by a crusher, ball milling or airflow crushing.
4. The process for preparing an eggshell iron-molybdenum catalyst containing silica as claimed in claim 1, wherein: the silicon dioxide is nano-scale silicon dioxide, and silica sol or gas-phase hydrophilic white carbon black is selected.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114931955A (en) * 2022-05-25 2022-08-23 西南化工研究设计院有限公司 High-temperature-resistant catalyst for preparing formaldehyde by methanol oxidation and preparation method thereof

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