A composite catalyst and its application in the preparation of paraformaldehyde

Abstract

The present application discloses a composite catalyst and its application in the preparation of paraformaldehyde. The catalyst is composed of an active metal and a support. The active metal is uniformly distributed on the surface of the support. Metal ions and formaldehyde molecules are bonded through metal bonds, reducing the activity of formaldehyde molecules and avoiding the formation of high polymers. In addition to supporting the active components, the support can form a synergistic catalytic effect with the active metal due to its inherent weak acidity. It can block the end groups of the polymer when the degree of polymerization of paraformaldehyde reaches a certain level, free the residual water, and quickly evaporate and dry. The catalyst is prepared by an impregnation method, with a simple preparation method, recyclable and reusable, reducing production costs. The system does not use acidic or alkaline additives, does not corrode equipment, reduces production investment, and further reduces production costs. The paraformaldehyde prepared by the method provided by the present invention has a low degree of polymerization, a high yield, and high product stability. The present application belongs to the technical field of chemical engineering.

Description

Technical Field

[0001] This application belongs to the field of chemical engineering technology, and in particular relates to a composite catalyst and its application in the preparation of paraformaldehyde. Background Art

[0002] Low-polymerization-degree paraformaldehyde (PF) is an important chemical raw material in industry. It has the characteristics of high aldehyde content, good water solubility, complete depolymerization, loose product, uniform particles, etc., which are convenient for storage and transportation. It is an ideal substitute for industrial formaldehyde and is widely used in fields such as chemical engineering, pharmaceuticals, pesticides, coatings, and resin synthesis, especially in the synthesis fields that require the use of anhydrous or high-concentration formaldehyde as raw materials. Since ordinary industrial formaldehyde contains more than 60% water, it not only increases the transportation volume and cost, but also increases the equipment investment due to the presence of water in the production of chemical products, reduces the reaction rate, and increases energy consumption and material consumption. According to relevant data reports, using paraformaldehyde instead of industrial formaldehyde to produce resin can reduce material consumption by more than 10%. For every ton of formaldehyde consumed, the steam consumption decreases by 1.5 - 2 tons. In China, low-polymerization-degree paraformaldehyde is mainly used in the production of herbicides, insecticides, fungicides, and fumigants, accounting for about 70% of the total consumption of paraformaldehyde. The total annual demand is about 50,000 tons, and more than 80% of it depends on imports.

[0003] At present, the relatively mature production process routes of paraformaldehyde applied at home and abroad mainly include the following several types:

[0004] 1. The process of producing paraformaldehyde by drying with a vacuum rake dryer. Disadvantages: There are dead corners, discharging is troublesome, and the product is in a lump shape and difficult to crush. The production cycle is long. It belongs to the traditional old production process and has been basically phased out abroad. At present, only a few domestic manufacturers use this method to produce PF. 2. Producing paraformaldehyde by drying with a metal conveyor belt. Disadvantages: It occupies a large area, makes a lot of noise during operation, and the product needs to be crushed, and granular paraformaldehyde cannot be obtained directly. 3. Spray method. Disadvantages: Gas-solid separation is difficult, fine particle dust recovery is difficult, the thermal efficiency is not high, and the equipment volume is large. 4. Azeotropic distillation method. Due to problems such as the type of azeotropic agent, recovery, and process amplification, only a few manufacturers produce it at present.

[0005] According to literature reports, the common problems in paraformaldehyde production are: when formaldehyde is heated and dehydrated, polymerization and depolymerization occur simultaneously, formaldehyde is easily volatilized and lost, and the yield is low; due to low aldehyde content and high water content, the product is sticky and easy to agglomerate; the stability and water solubility are poor. The main reason is that during the storage process of the product, due to the presence of some polar substances (trace water and other impurities), paraformaldehyde will continue to polymerize, with a high degree of polymerization, large molecular weight, and difficult to dissolve; in addition, the product contains a small amount of formic acid and methanol, and a certain amount of insoluble paraformaldehyde ester will be produced under the catalysis of formic acid.

[0006] The key to preparing paraformaldehyde lies in controlling the degree of polymerization of the product, preventing the high polymerization of formaldehyde, shortening the drying and dehydration time, and increasing the product yield. Therefore, some effective strategies are needed to improve the yield of the formaldehyde polymerization reaction and enhance the stability of paraformaldehyde. Summary of the Invention

[0007] The purpose of the implementation of this application is to provide a composite catalyst and its application in the preparation of paraformaldehyde, so as to solve the technical problems of low degree of polymerization of paraformaldehyde, low yield, and poor product stability existing in the prior art during the preparation process.

[0008] To achieve the above purpose, the technical solution adopted in this application is: to provide a preparation method of a composite catalyst, which specifically includes the following steps:

[0009] In deionized water, add metal salts, and after dissolution, add a carrier, mix, stir, and dry to obtain a composite catalyst;

[0010] The metal salts are one or more of hydrochlorides, sulfates, nitrates, acetylacetonate salts, and their hydrates of Fe;

[0011] The carriers are one or more of SiO2 molecular sieves, Al2O3 molecular sieves, HZSM-5 molecular sieves, and Hβ molecular sieves.

[0012] In one embodiment,

[0013] The mass ratio of the metal element of the metal salt to the mass of the carrier is 0.03 - 0.09 : 1.

[0014] In one embodiment,

[0015] The mixing temperature is 40 - 60 °C.

[0016] In one embodiment,

[0017] The stirring time is 4 - 6 h.

[0018] In one embodiment,

[0019] The metal salts are specifically one or more of ferric chloride hexahydrate (FeCl3·6H2O), ammonium iron(II) sulfate dodecahydrate (NH4Fe(SO4)2·12H2O), ferrous sulfate heptahydrate (FeSO4·7H2O), ferric chloride (FeCl3), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), ferrous chloride (FeCl2), iron(III) acetylacetonate (Fe(acac)3), or ferric sulfate (Fe2(SO4)3).

[0020] The present application also provides an application of a composite catalyst in the preparation of paraformaldehyde, which specifically includes the following steps: In a reactor, methanol is added, and using a formaldehyde solution as a raw material, a polymerization reaction is carried out in the presence of the composite catalyst to obtain paraformaldehyde.

[0021] In one embodiment,

[0022] The mass ratio of the composite catalyst to the formaldehyde solution is 0.01 - 0.07 : 1.

[0023] In one embodiment,

[0024] The temperature of the polymerization reaction is 60 - 120 °C, and the time of the polymerization reaction is 1 - 3 h.

[0025] In one embodiment,

[0026] The mass ratio of methanol to the formaldehyde solution is 1 : 1.

[0027] In one embodiment,

[0028] The concentration of the formaldehyde solution is 37 - 75 %.

[0029] The present application provides a preparation method of a composite catalyst. This catalyst is composed of an active metal and a carrier. The active metal is uniformly distributed on the surface of the carrier. Metal ions and formaldehyde molecules are combined through metal bonds, reducing the activity of formaldehyde molecules and avoiding the formation of high polymers. In addition to supporting the active component, the carrier can form a synergistic catalytic effect with the active metal due to its inherent weak acidity. It can seal the end groups of the polymer when the degree of polymerization of paraformaldehyde reaches a certain level, making the residual water free and evaporating and drying quickly. The catalyst is prepared by an impregnation method, with a simple preparation method, recyclable and reusable, reducing the production cost. The present application also provides an application of the composite catalyst in the preparation of paraformaldehyde. This method does not use acidic or alkaline auxiliaries, does not corrode equipment, reduces the production investment, and further reduces the production cost. The paraformaldehyde prepared by the method provided by the present invention has a low degree of polymerization, a high yield, and high product stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 It is an electron microscope photograph of the composite catalyst. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, this application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0033] Example 1

[0034] (1) In 50 ml of deionized water, add 4.84 g of FeCl3·6H2O. After complete dissolution, add 20 g of HZSM-5 molecular sieve. Heat up to 40 °C and keep stirring for 5 h. Evaporate and remove the excess water by distillation. After sufficient drying, a composite catalyst is obtained, denoted as 1# catalyst. The structural characterization is as Figure 1 shown, instrument model: JEOL JSM-6701F, magnified 5000 times;

[0035] (2) In a reaction vessel, sequentially add 100 g of 37% formaldehyde solution and 1.85 g of 1# catalyst. After raising the temperature to 80 °C, add 100 g of methanol, stir and mix for polymerization reaction, and keep the reaction at a constant temperature for 2 h to obtain a reaction product. Pump this reaction product to a multi-stage fluidized bed series spray drying system for drying to obtain paraformaldehyde solid particles. The paraformaldehyde content of the final product is 93.2%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0036] Example 2

[0037] The difference between this example and Example 1 is that FeCl3·6H2O is replaced with NH4Fe(SO4)2·12H2O, and the addition amount of NH4Fe(SO4)2·12H2O is 8.634 g, denoted as 2# catalyst. Use the 2# catalyst for the polymerization reaction. The paraformaldehyde content of the final product is 93.0%, the degree of polymerization is 14, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0038] Example 3

[0039] The difference between this example and Example 1 is that FeCl3·6H2O is replaced with FeSO4·7H2O, and the addition amount of FeSO4·7H2O is 4.978 g, denoted as 3# catalyst. Use the 3# catalyst for the polymerization reaction. The paraformaldehyde content of the final product is 94.3%, the degree of polymerization is 9, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0040] Example 4

[0041] The difference between this example and Example 3 is that in step (ii), the concentration of the formaldehyde solution is 50%, the addition amount of the 3# catalyst is 2.5 g, the paraformaldehyde content of the final product is 95.5%, the degree of polymerization is 14, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0042] Example 5

[0043] The difference between this example and Example 3 is that in step (ii), the concentration of the formaldehyde solution is 75%, the addition amount of the 3# catalyst is 3.75 g, the paraformaldehyde content of the final product is 95.9%, the degree of polymerization is 16, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0044] Example 6

[0045] The difference between this example and Example 3 is that in step (ii), the addition amount of the 3# catalyst is 0.37 g, the paraformaldehyde content of the final product is 92.6%, the degree of polymerization is 16, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0046] Example 7

[0047] The difference between this example and Example 3 is that in step (ii), the addition amount of the 3# catalyst is 1.11 g, the paraformaldehyde content of the final product is 93.6%, the degree of polymerization is 12, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0048] Example 8

[0049] The difference between this example and Example 3 is that in step (ii), the addition amount of the 3# catalyst is 2.59 g, the paraformaldehyde content of the final product is 95.5%, the degree of polymerization is 14, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0050] Example 9

[0051] The difference between this example and Example 3 is that in step (ii), after adding the 3# catalyst, the temperature is raised to 60 °C, the paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 10, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0052] Example 10

[0053] The difference between this example and Example 3 is that in step (ii), after adding the 3# catalyst, the temperature is raised to 100 °C, the paraformaldehyde content of the final product is 95.5%, the degree of polymerization is 20, and after being placed at room temperature for 90 days, the solubility of the product in water is 100%.

[0054] Example 11

[0055] The difference between this example and Example 3 is that in step (ii), after adding catalyst #3, the temperature is raised to 120 °C. The paraformaldehyde content of the final product is 96.6%, the degree of polymerization is 25, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0056] Example 12

[0057] The difference between this example and Example 3 is that in step (ii), the polymerization reaction time is 1 h. The paraformaldehyde content of the final product is 93.7%, the degree of polymerization is 9, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0058] Example 13

[0059] The difference between this example and Example 3 is that in step (ii), the polymerization reaction time is 3 h. The paraformaldehyde content of the final product is 95.4%, the degree of polymerization is 14, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0060] Example 14

[0061] The difference between this example and Example 1 is that FeCl3·6H2O is replaced with Fe2(SO4)3, and the addition amount of Fe2(SO4)3 is 7.16 g, denoted as catalyst #4. Polymerization reaction is carried out using catalyst #4. The paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0062] Example 15

[0063] The difference between this example and Example 1 is that FeCl3·6H2O is replaced with FeCl3, and the addition amount of FeCl3 is 2.904 g, denoted as catalyst #5. Polymerization reaction is carried out using catalyst #5. The paraformaldehyde content of the final product is 94.4%, the degree of polymerization is 12, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0064] Example 16

[0065] The difference between this example and Example 1 is that FeCl3·6H2O is replaced with Fe(NO3)3·9H2O, and the addition amount of Fe(NO3)3·9H2O is 7.234 g, denoted as catalyst #6. Polymerization reaction is carried out using catalyst #6. The paraformaldehyde content of the final product is 93.6%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0066] Example 17

[0067] The difference between this example and Example 1 is that FeCl3·6H2O is replaced by FeCl2, and the addition amount of FeCl2 is 2.269 g, denoted as catalyst No. 7. Polymerization reaction is carried out using catalyst No. 7. The paraformaldehyde content of the final product is 93.8%, the degree of polymerization is 14, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0068] Example 18

[0069] The difference between this example and Example 1 is that FeCl3·6H2O is replaced by Fe(acac)3, and the addition amount of Fe(acac)3 is 6.324 g, denoted as catalyst No. 8. Polymerization reaction is carried out using catalyst No. 8. The paraformaldehyde content of the final product is 93%, the degree of polymerization is 16, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0070] Example 19

[0071] The difference between this example and Example 3 is that the HZSM-5 molecular sieve is replaced by SiO2 molecular sieve, denoted as catalyst No. 9. Polymerization reaction is carried out using catalyst No. 9. The paraformaldehyde content of the final product is 93.2%, the degree of polymerization is 16, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0072] Example 20

[0073] The difference between this example and Example 3 is that the HZSM-5 molecular sieve is replaced by Al2O3 molecular sieve, denoted as catalyst No. 10. Polymerization reaction is carried out using catalyst No. 10. The paraformaldehyde content of the final product is 93.5%, the degree of polymerization is 14, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0074] Example 21

[0075] The difference between this example and Example 3 is that the HZSM-5 molecular sieve is replaced by Hβ molecular sieve, denoted as catalyst No. 11. Polymerization reaction is carried out using catalyst No. 11. The paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 16, and after standing at room temperature for 90 days, the solubility of this product in water is 100%.

[0076] Example 22

[0077] This example is different from Example 3 in that the addition amount of FeSO4·7H2O is 2.987 g, denoted as catalyst No. 12. Polymerization reaction is carried out using catalyst No. 12. The paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 16, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0078] Example 23

[0079] This example is different from Example 3 in that the addition amount of FeSO4·7H2O is 6.969 g, denoted as catalyst No. 13. Polymerization reaction is carried out using catalyst No. 13. The paraformaldehyde content of the final product is 95.2%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0080] Example 24

[0081] This example is different from Example 3 in that the addition amount of FeSO4·7H2O is 8.96 g, denoted as catalyst No. 14. Polymerization reaction is carried out using catalyst No. 14. The paraformaldehyde content of the final product is 95.7%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0082] Example 25

[0083] This example is different from Example 3 in that in step (i), after adding the molecular sieve, the temperature is raised to 50 °C, denoted as catalyst No. 15. Polymerization reaction is carried out using catalyst No. 15. The paraformaldehyde content of the final product is 94%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0084] Example 26

[0085] This example is different from Example 3 in that in step (i), after adding the molecular sieve, the temperature is raised to 60 °C, denoted as catalyst No. 16. Polymerization reaction is carried out using catalyst No. 16. The paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 10, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0086] Example 27

[0087] This example is different from Example 3 in that in step (i), the holding and stirring time is 4 h, denoted as catalyst No. 17. Polymerization reaction is carried out using catalyst No. 17. The paraformaldehyde content of the final product is 94%, the degree of polymerization is 16, and after standing at room temperature for 90 days, the solubility of the product in water is 100%.

[0088] Example 28

[0089] The difference between this example and Example 3 is that in step (i), the heat preservation and stirring time is 6 h, denoted as 18# catalyst. Polymerization reaction is carried out using the 18# catalyst. The paraformaldehyde content of the final product is 94.1%, the degree of polymerization is 14. After being placed at room temperature for 90 days, the solubility of this product in water is 100%.

[0090] Example 29

[0091] Example of catalyst recycling: Load the 3# catalyst into a fixed-bed reactor and heat it up to 80 °C for heat preservation. At room temperature, prepare a mixed solution of 1200 g of 37% formaldehyde solution and 1200 g of methanol and preheat it to 60 °C. Feed the preheated mixed solution into the fixed-bed reactor at a flow rate of 20 ml / min. After circulating and reacting for 2 h, discharge the product and pump it to a multi-stage fluidized bed series spray drying system for drying to obtain paraformaldehyde solid particles. The paraformaldehyde content of the final product is 94.2%, the degree of polymerization is 9. After being placed at room temperature for 90 days, the solubility of this product in water is 100%.

[0092] Comparative Example 1

[0093] In a reaction vessel, sequentially add 100 g of 37% formaldehyde solution and 1.85 g of HZSM-5 molecular sieve. After raising the temperature to 80 °C, add 100 g of methanol, stir and mix, and keep the reaction at a constant temperature for 2 h to obtain a reaction product. Pump the reaction product to a multi-stage fluidized bed series spray drying system for drying to obtain paraformaldehyde solid particles. The paraformaldehyde content of the final product is 94.8%, the degree of polymerization is 35. After being placed at room temperature for 90 days, the solubility of this product in water is 80%.

[0094] Comparative Example 2

[0095] In a reaction vessel, sequentially add 100 g of 37% formaldehyde solution and 1.85 g of FeSO4·7H2O. After raising the temperature to 80 °C, add 100 g of methanol, stir and mix, and keep the reaction at a constant temperature for 2 h to obtain a reaction product. Pump the reaction product to a multi-stage fluidized bed series spray drying system for drying to obtain paraformaldehyde solid particles. The paraformaldehyde content of the final product is 95.3%, the degree of polymerization is 40. After being placed at room temperature for 90 days, the solubility of this product in water is 75%.

[0096] It can be seen from Examples 1-28 and Comparative Examples 1-2 that the effects are not as good as those of the composite catalyst when only adding a carrier or a metal salt.

[0097] The present application provides a method for preparing a composite catalyst. In deionized water, a metal salt is added. After dissolution, a carrier is added. After mixing, stirring, and drying, the composite catalyst is obtained. The catalyst is composed of an active metal and a carrier. The active metal is uniformly distributed on the surface of the carrier. Metal ions and formaldehyde molecules are bonded through metal bonds, reducing the activity of formaldehyde molecules and preventing the formation of polymers. In addition to supporting the active components, the carrier can form a synergistic catalytic effect with the active metal due to its inherent weak acidity. When the degree of polymerization of paraformaldehyde reaches a certain level, it can block the end groups of the polymer, freeing the residual water, which can then be quickly evaporated and dried. The catalyst is prepared by an impregnation method, with a simple preparation method, recyclable and reusable, reducing production costs. The present application also provides the application of the composite catalyst in the preparation of paraformaldehyde. In a reactor, using a formaldehyde solution as a raw material, a polymerization reaction is carried out in the presence of the composite catalyst to obtain paraformaldehyde. This method does not use acidic or alkaline auxiliaries, does not corrode equipment, reduces production investment, and further reduces production costs. The paraformaldehyde prepared by the method provided by the present invention has a low degree of polymerization, a high yield, and high product stability.

[0098] In addition, the terms "first" and "second" are used for descriptive purposes only 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 of" means two or more unless otherwise specifically defined.

[0099] The foregoing is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. Application of a composite catalyst in the preparation of paraformaldehyde, characterized in that Specifically, it includes the following steps: In a reactor, methanol is added, and using a formaldehyde solution as a raw material, a polymerization reaction is carried out in the presence of a composite catalyst to obtain paraformaldehyde; The preparation method of the composite catalyst includes the following steps: In deionized water, a metal salt is added, and after dissolution, a carrier is added. After mixing, stirring, and drying, a composite catalyst is obtained; The metal salt is one or more of ferric chloride, ferrous sulfate, ferric nitrate, ferric acetylacetonate, and their hydrates; The carrier is one or more of SiO2 molecular sieve, Al2O3 molecular sieve, HZSM-5 molecular sieve, and Hβ molecular sieve; The mass ratio of the metal element of the metal salt to the mass of the carrier is 0.03 - 0.09 : 1; The temperature of the mixing is 40 - 60 °C.

2. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The mass ratio of the composite catalyst to the formaldehyde solution is 0.01 - 0.07 :

1.

3. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The temperature of the polymerization reaction is 60 - 120 °C, and the time of the polymerization reaction is 1 - 3 h.

4. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The mass ratio of methanol to the formaldehyde solution is 1 :

1.

5. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The concentration of the formaldehyde solution is 37 - 75 %.

6. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The time of the stirring is 4 - 6 h.

7. Use of a composite catalyst according to claim 1 in the preparation of paraformaldehyde, characterized in that, The metal salt is specifically one or more of ammonium ferric sulfate dodecahydrate, ferrous sulfate heptahydrate, ferric chloride, ferric nitrate nonahydrate, ferrous chloride, ferric acetylacetonate, or ferric sulfate.

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