A method for synthesizing dipentaerythritol and composite materials thereof

Abstract

The present application relates to the technical field of fine chemical industry, and provides a method for synthesizing dipentaerythritol and a composite material thereof.Ammonia-rich mesoporous molecular sieve is mixed with alkaline oxide in proportion, and then formaldehyde is adsorbed to obtain a composite material reversibly loaded with formaldehyde.In the reaction, acetaldehyde or a mixed solution of acetaldehyde and formaldehyde is put into a reactor at one time, the above composite material is added, and then an alkali solution is continuously or in batches added to the system at a controlled rate, formaldehyde is slowly released from the composite material into the reaction system, and the condensation reaction of acetaldehyde and formaldehyde occurs under low-temperature conditions to directionally generate dipentaerythritol.After the reaction is completed, the composite material is recovered by filtration and can be recycled after calcination.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and more specifically, to a method for synthesizing dipentaerythritol and its composite material. Background Technology

[0002] Dipentaerythritol (Di-penta) is a highly functional polyol containing six hydroxyl groups. Compared to pentaerythritol (Penta), which contains four hydroxyl groups, its higher hydroxyl density gives it a significant advantage in high-end applications such as high-grade flame-retardant coatings, aviation lubricants, and epoxy resin curing agents. Its market price is 30-50% higher than that of pentaerythritol. Industrially, formaldehyde, acetaldehyde, and alkali are typically used as raw materials to co-produce mono-, di-, and tri-pentaerythritols via a condensation reaction. Dipentaerythritol exists as a byproduct in the reaction system, with a selectivity of only 1-3 wt%. This results in low raw material utilization and high separation costs, making it difficult to meet the continuously growing market demand for high-purity dipentaerythritol. Therefore, how to improve the synthetic selectivity of dipentaerythritol without significantly sacrificing the pentaerythritol yield is a core technical challenge that urgently needs to be solved in this field.

[0003] To address the aforementioned issues, several existing technologies have been explored. CN115231990B (Chongqing Yuntianhua Tianju New Materials Co., Ltd., Qiu Youping et al., 2022) discloses a method for preparing high-purity dipentaerythritol, which uses a tubular reactor to add formaldehyde dropwise under high temperature and reflux conditions of 120-140℃ for a long time (4-8h). The method utilizes the localized formaldehyde deficiency in the reaction system to induce the formation of dipentaerythritol, thereby increasing the selectivity of dipentaerythritol to 5-9wt%. However, under high-temperature reflux conditions, formaldehyde is highly susceptible to self-polymerization, and the generated polyoxymethylene (POM) easily clogs the pipeline, requiring periodic shutdowns for cleaning, severely impacting production continuity. Simultaneously, the high-temperature, highly corrosive environment increases the equipment corrosion rate by 3-5 times, with the annual corrosion rate of 316L stainless steel equipment exceeding 0.5mm, significantly increasing equipment maintenance costs. Furthermore, the tubular reactor requires high investment, is difficult to scale up industrially, and reduces the pentaerythritol yield by 10-15%, resulting in limited overall economic benefits. CN119822931A (Tsinghua University, Luo Guangsheng et al., 2025) discloses a highly selective continuous synthesis method for bispentaerythritol. This method increases the collision probability between pentaerythritol and trimethylolacetaldehyde in the liquid phase by introducing pentaerythritol exogenously into the system at the initial stage of the reaction, thereby promoting intermolecular dehydration condensation to generate bispentaerythritol and improving its selectivity to 4-6 wt%. However, this method requires continuous exogenous replenishment of pentaerythritol, resulting in a 8-12% decrease in the single-pass yield of the main product, pentaerythritol. Furthermore, the post-reaction processing requires an additional crystallization-recrystallization unit to separate excess pentaerythritol, extending the process flow and significantly increasing energy consumption. In summary, the aforementioned existing technologies all face common problems such as a significant decrease in pentaerythritol yield, formaldehyde self-polymerization, and equipment corrosion. Moreover, none of them address the technical path of pre-adsorbing and storing formaldehyde in a carrier material in the form of chemical bonds, followed by controlled and slow release during the reaction. To date, there have been no reports on the use of the "pre-adsorption-post-slow release of formaldehyde" strategy to improve the selectivity of dipentaerythritol synthesis. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of existing technologies, this invention provides a method for synthesizing dipentaerythritol and its composite material. A reversibly formaldehyde-loaded composite material is prepared by mixing an amino-rich mesoporous molecular sieve with an alkaline oxide to adsorb formaldehyde. During the reaction, acetaldehyde is added in a single step, followed by a controlled addition of alkaline solution, allowing formaldehyde to be slowly released into the system and directionally generated into dipentaerythritol. This solves the problems of pipe blockage, equipment corrosion, and decreased pentaerythritol yield caused by high-temperature dropwise addition of formaldehyde in existing technologies.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for synthesizing dipentaerythritol includes the following steps: Step 1: Prepare composite material, which includes amino-rich mesoporous molecular sieve, basic oxide and formaldehyde; Step 2: Add acetaldehyde or an acetaldehyde-formaldehyde mixture into the reactor in one go, and then add the composite material obtained in Step 1 into the reactor; Step 3: Add alkali continuously or in batches to the reactor at a controlled rate to generate dipentaerythritol. After the reaction is completed, filter and recover the composite material. Step four: calcine the composite material recovered in step three to regenerate it. Then, impregnate the regenerated composite material with formaldehyde solution again to load it with formaldehyde as described in step one, and return it to step two for recycling.

[0006] As a further aspect of the present invention, in step one, the specific preparation steps of the composite material include: mixing an amino-rich mesoporous molecular sieve with an alkaline oxide to adsorb formaldehyde, thereby obtaining a composite material, wherein the amino groups of the amino-rich mesoporous molecular sieve form imine bonds and hemiacetal bonds with formaldehyde, thereby reversibly loading formaldehyde into the composite material.

[0007] As a further aspect of the present invention, in step one, the composite material further includes a hydrophobic surface treatment agent; by mass percentage, the amount of amino-rich mesoporous molecular sieve added is 60-80%; the amount of alkaline oxide added is 5-15%; the amount of formaldehyde added is 10-25%; and the amount of hydrophobic surface treatment agent added is 0-5%.

[0008] As a further embodiment of the present invention, in step two, the initial concentration of acetaldehyde in the reactor is greater than or equal to 0.15 mol / L, and the molar ratio of formaldehyde to acetaldehyde does not exceed 3:1; in step three, the reaction temperature is 30-50℃, and the alkali addition time is 0.5-3h; in step four, the calcination temperature is 200-300℃, and the calcination time is 0.5-4h.

[0009] As a further embodiment of the present invention, the amino-rich mesoporous molecular sieve has a pore size of 2-5 nm and a specific surface area of ​​not less than 500 m² / g.

[0010] As a further embodiment of the present invention, the alkali in step three is NaOH, KOH, or a mixed aqueous solution thereof, and the total amount of alkali added is expressed as OH... - The molar amount is 0.8-1.5 times that of acetaldehyde.

[0011] As a further embodiment of the present invention, the alkaline oxide is one or more of MgO, CaO, and ZnO.

[0012] A composite material for synthesizing dipentaerythritol, comprising, by mass percentage, 60-80% amino-rich mesoporous molecular sieve, 5-15% basic oxide, 10-25% formaldehyde and 0-5% hydrophobic surface treatment agent.

[0013] As a further aspect of the present invention, the saturated adsorption capacity of the composite material for formaldehyde under sealed conditions at 25°C is greater than or equal to 0.15 g / g.

[0014] As a further aspect of the present invention, the formaldehyde removal rate of the composite material is greater than or equal to 78% after calcination at 250°C for 2 hours.

[0015] Compared with the prior art, the beneficial effects of the method for synthesizing bispentaerythritol and its composite material of the present invention are as follows: This invention pre-adsorbs formaldehyde onto an amino-rich mesoporous molecular sieve to create a composite material, which is then slowly released in an alkaline reaction system, ensuring the entire reaction is conducted at a low temperature of 30-50°C. Existing technologies use high-temperature reflux to add formaldehyde dropwise, which leads to formaldehyde clogging of pipelines and a significant increase in equipment corrosion rates. This method fundamentally avoids these problems through a solid-state slow-release strategy, and eliminates the need for specialized equipment such as tubular reactors, allowing the direct use of existing batch reaction devices.

[0016] This invention controls the slow release rate of formaldehyde, ensuring that the transient concentration of formaldehyde in the reaction system remains below stoichiometry. This induces a directed intermolecular dehydration condensation between trimethylolacetaldehyde and pentaerythritol, resulting in a more than 5-fold increase in pentaerythritol selectivity compared to traditional methods. Furthermore, the decrease in pentaerythritol yield is more controllable in this method, leading to less overall yield loss.

[0017] The composite material used in this invention can be recovered from the reaction solution by filtration and can be regenerated by calcination at 200-300℃ for 0.5-4 hours. After being recycled 5 times, the selectivity of dipentaerythritol can still be maintained at more than 80% of the initial value. No additional raw materials or new waste treatment units are required, which has a certain industrial application basis. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for synthesizing dipentaerythritol according to the present invention.

[0019] Figure 2 The formaldehyde adsorption kinetics curve of the MCM-41-NH2 composite material provided by the present invention at 25°C.

[0020] Figure 3 Cyclic curves of the MCM-41-NH2 composite material provided by the present invention. Detailed Implementation

[0021] The technical solutions of this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] Example 1

[0023] Step 1: Preparation of formaldehyde-loaded composite material: 80g of MCM-41-NH2 (pore size 2.7nm, BET specific surface area 650m² / g) and 10g of MgO were mixed evenly in a mortar. The mixed solid was then completely immersed in 30g of a 36% formaldehyde aqueous solution and impregnated at 25℃ for 2 hours. This allowed formaldehyde molecules to chemically bind to the surface of the composite material by forming reversible imine and hemiacetal bonds with the amino groups on the surface of MCM-41-NH2, thereby fixing the formaldehyde in the composite material in a chemical storage form. After impregnation, approximately 105g of formaldehyde-loaded composite material was obtained, with a formaldehyde loading of 0.19g / g (i.e., approximately 0.19g of formaldehyde is loaded per gram of composite material, and the formaldehyde mass accounts for 19% of the total mass of the composite material).

[0024] Step 2, Reaction: 7.2 g (0.16 mol) of acetaldehyde and 60 g of deionized water were added sequentially to a 500 mL four-necked flask. After stirring thoroughly, 53 g of the formaldehyde-loaded composite material obtained in Step 1 (containing approximately 0.32 mol of formaldehyde, i.e., a formaldehyde / acetaldehyde molar ratio of 2:1) was added to the flask all at once. This ensures that the slow-release formaldehyde coexists with acetaldehyde at a concentration lower than the stoichiometric ratio in the initial stage of the reaction, thus creating kinetic conditions for the subsequent selective synthesis of dipentaerythritol. The reaction system was heated to 35 °C, and 16 g of a 50% NaOH solution was added dropwise in controlled batches over a period of 2 hours. After the NaOH solution was completely added, the mixture was kept at 35 °C for another 1 hour to ensure complete reaction, yielding a reaction mixture containing dipentaerythritol.

[0025] Step 3, Post-processing: After removing the solid composite material from the reaction mixture containing dipentaerythritol obtained in Step 2 through solid-liquid separation, an appropriate amount of dilute acid was added to the filtrate for neutralization, adjusting the pH to neutral to terminate the condensation reaction and prevent further decomposition of the product under alkaline conditions. The neutralized material was then sent to an evaporator for evaporation and concentration to remove a large amount of water and increase the product concentration. The concentrated material was then recrystallized with methanol, utilizing the difference in solubility of dipentaerythritol and pentaerythritol in methanol to achieve preliminary separation. After filtration and drying, the dipentaerythritol product was obtained. High-performance liquid chromatography (HPLC) analysis showed that the dipentaerythritol selectivity in the obtained product was 11.2 wt%, the pentaerythritol content was 74.8 wt%, and the formaldehyde volatilization loss during the reaction was only 1.0%, indicating that the formaldehyde-loaded composite material described in this embodiment has a good formaldehyde sequestration effect and effectively reduces the release of formaldehyde into the environment.

[0026] Step 4, Composite Material Regeneration: The formaldehyde-loaded composite material solid obtained from the solid-liquid separation in Step 3 is placed in a tube furnace and calcined at 250°C for 2 hours to fully decompose and remove the organic residues attached to the surface of the composite material, thereby restoring the amino active sites of MCM-41-NH2 and obtaining the regenerated composite material. The regenerated composite material is then impregnated with formaldehyde solution again according to the method described in Step 1 for formaldehyde loading, and the operations of Steps 2 and 3 are repeated for a total of 5 cycles. The dipentaerythritol selectivity corresponding to each cycle number is detected, such as... Figure 3 As shown, after 5 cycles, the selectivity of dipentaerythritol decreased from the initial 11.2% to 9.5%, a decrease of about 1.7 percentage points, indicating good cycle stability. This shows that the formaldehyde-loaded composite material described in this invention can be stably recycled after calcination and regeneration at 250°C, and has good potential for industrial application.

[0027] like Figure 2 The figure shows the formaldehyde adsorption kinetics curve of the MCM-41-NH2 composite material at 25℃. It can be seen that as the value of the horizontal axis increases, the adsorption amount shows a rapid upward trend in the early stage. Then the slope of the increase gradually decreases. When the value of the horizontal axis reaches the range of 20-25, the curve gradually flattens and reaches the saturation state. Finally, the adsorption amount stabilizes at about 200mg / g.

[0028] Example 2

[0029] Step 1: Preparation of formaldehyde-loaded composite material: 80g of SBA-15-NH2 and 10g of MgO were mixed evenly in a mortar. The mixed solid was then completely immersed in 30g of a 36% (w / w) formaldehyde aqueous solution and impregnated at 25°C for 2 hours. This process allowed formaldehyde molecules to chemically bond to the surface of the composite material by forming reversible imine and hemiacetal bonds with the amino groups on the surface of SBA-15-NH2. After impregnation, the formaldehyde-loaded composite material was obtained.

[0030] Step 2, condensation reaction: 7.2 g (0.16 mol) of acetaldehyde and 60 g of deionized water were added sequentially to a 500 mL four-necked flask. After stirring evenly, 53 g of the formaldehyde-loaded composite material obtained in Step 1 was added to the four-necked flask all at once. The reaction system was heated to 35 °C, and 16 g of 50% NaOH solution was added dropwise to the reaction system in batches at a controlled rate for 2 h. After the NaOH solution was added, the mixture was kept at 35 °C for another 1 h to obtain a reaction mixture containing dipentaerythritol. The operating parameters in Step 2 were exactly the same as in Example 1, except that the amino-rich mesoporous molecular sieve in the formaldehyde-loaded composite material was replaced by SBA-15-NH2 instead of MCM-41-NH2 to investigate the effect of different amino-rich mesoporous molecular sieves on the selectivity of dipentaerythritol synthesis.

[0031] Step 3, Post-processing: After removing the composite material solid from the reaction mixture containing dipentaerythritol obtained in Step 2 through solid-liquid separation, an appropriate amount of dilute acid was added to the filtrate for neutralization, and the pH was adjusted to neutral. The neutralized material was then concentrated by evaporation, and methanol was added for recrystallization. After filtration and drying, the dipentaerythritol product was obtained. High-performance liquid chromatography (HPLC) analysis showed that the selectivity of dipentaerythritol in the obtained product was 10.8 wt%.

[0032] Step 4, Composite Material Regeneration: The solid composite material obtained from the solid-liquid separation in Step 3 is placed in a tube furnace and calcined at 250°C for 2 hours to fully decompose and remove the organic residues attached to the surface of the composite material, thereby restoring the amino active sites of SBA-15-NH2 and obtaining the regenerated composite material. The regenerated composite material can be reloaded with formaldehyde and recycled according to the method described in Step 1.

[0033] Example 3

[0034] Step 1, Preparation of hybrid support and formaldehyde-loaded composite material: In this embodiment, a hybrid support composed of UiO-66-NH2 nanocrystals and SBA-15-NH2 is used as an amino-rich mesoporous molecular sieve. The specific operation is as follows.

[0035] First, UiO-66-NH2 nanocrystals (80 nm in diameter, BET specific surface area 1100 m² / g) and SBA-15-NH2 (1 μm in diameter, BET specific surface area 650 m² / g) were weighed separately at a mass ratio of 30:70 and placed in the same container. An appropriate amount of anhydrous ethanol was added, and the mixture was ultrasonically dispersed into a uniform suspension. Subsequently, the suspension was placed in an 80°C water bath and the ethanol was evaporated while stirring, so that the UiO-66-NH2 nanocrystals were uniformly dispersed and embedded in the mesoporous channels and interparticle gaps of SBA-15-NH2, thus obtaining a hybrid support of UiO-66-NH2 and SBA-15-NH2.

[0036] Next, the above-mentioned hybrid support was added to an anhydrous toluene solution containing an appropriate amount of 3-aminopropyltrimethoxysilane (APTES) and refluxed at 110°C for 4 hours. After the reaction was completed, the unreacted APTES and byproduct methanol were removed by filtration and washing with anhydrous ethanol. The mixture was then dried in a vacuum oven to obtain a hybrid support with secondary amino functionalization. Its amino density was measured to be 2.1 mmol / g, which is significantly higher than that of MCM-41-NH2 in Example 1, which is beneficial to further enhance the reversible adsorption capacity for formaldehyde.

[0037] Finally, the above-mentioned secondary amino-functionalized hybrid carrier was immersed in a 36% formaldehyde aqueous solution at 25°C for 2 hours for adsorption, so that formaldehyde was bound to the surface of the composite material by forming reversible imine bonds and hemiacetal bonds with the amino groups on the surface of the hybrid carrier. After impregnation, the free formaldehyde liquid was removed by filtration, and the residual physically adsorbed formaldehyde was removed by purging with nitrogen for 3 minutes to obtain the formaldehyde-loaded composite material, namely the "HCHO@UiO-SBA-NH2" composite, and the formaldehyde loading was determined to be 0.14 g / g.

[0038] Step 2, condensation reaction: 7.2 g (0.16 mol) of acetaldehyde and 60 g of deionized water were added sequentially to a 500 mL four-necked flask. After stirring evenly, the formaldehyde-loaded composite material "HCHO@UiO-SBA-NH2" obtained in Step 1 was added to the four-necked flask all at once. After heating the reaction system to 35 °C, 16 g of 50% NaOH solution was added dropwise to the reaction system in batches at a controlled rate, with the addition time controlled at 2 h. After the NaOH solution was added, the temperature was maintained at 35 °C for another 1 h to obtain a reaction mixture containing dipentaerythritol. Except that the formaldehyde-loaded composite material was replaced with "HCHO@UiO-SBA-NH2" prepared in this example, the other operating parameters were exactly the same as in Step 2 of Example 1.

[0039] Step 3, Post-processing: After removing the composite material solid from the reaction mixture containing dipentaerythritol obtained in Step 2 through solid-liquid separation, an appropriate amount of dilute acid was added to the filtrate for neutralization, and the pH was adjusted to neutral. The neutralized material was then concentrated by evaporation, and methanol was added for recrystallization. After filtration and drying, the dipentaerythritol product was obtained. High-performance liquid chromatography (HPLC) analysis showed that the selectivity of dipentaerythritol in the obtained product was 9.8 wt%, and the formaldehyde volatilization loss was 1.5%.

[0040] Step 4, Composite Material Regeneration and Recycling: The solid "HCHO@UiO-SBA-NH2" composite material obtained from solid-liquid separation in Step 3 was placed in a tube furnace and calcined at 250℃ for 2 hours to fully decompose and remove the organic residues attached to the surface of the composite material, restoring the amino active sites. The regenerated composite material was characterized, and the amino recovery rate was found to be 92%, indicating that most of the amino functional groups on the hybrid support were retained after calcination at 250℃, and the regeneration effect was good. The regenerated composite material was impregnated with formaldehyde solution again according to the method described in Step 1 for formaldehyde loading, and the operations of Steps 2 and 3 were repeated for a total of 5 cycles. The formaldehyde saturated adsorption capacity of the "HCHO@UiO-SBA-NH2" composite material after 5 cycles was measured. The results showed that the decrease in formaldehyde saturated adsorption capacity after 5 cycles was less than 8%, indicating good cycle stability and meeting the basic requirements for industrial reuse.

[0041] Comparative Example 1 To demonstrate the key role of the formaldehyde-loaded composite material slow-release formaldehyde strategy described in this invention in improving the selectivity of dipentaerythritol synthesis, the following comparative example 1 was set up: This comparative example uses the conventional process of directly adding free formaldehyde solution in a single step for reaction.

[0042] The specific operation is as follows: 7.2 g (0.16 mol) of acetaldehyde and 60 g of deionized water were added sequentially to a 500 mL four-necked flask. After stirring evenly, a 36% formaldehyde aqueous solution containing 0.12 mol of formaldehyde was added to the four-necked flask all at once. The reaction system was heated to 35°C, and 16 g of 50% NaOH solution was added dropwise in batches at a controlled rate over a period of 2 hours. After the NaOH solution was added, the mixture was kept at 35°C for another hour to obtain a reaction mixture containing dipentaerythritol. The reaction mixture was neutralized to pH neutral by adding an appropriate amount of dilute acid, then concentrated by evaporation, recrystallized from methanol, filtered, and dried to obtain the dipentaerythritol product. High-performance liquid chromatography (HPLC) analysis showed that the selectivity of dipentaerythritol in the product was only 2.1 wt%, and the pentaerythritol content was 89.2 wt%.

[0043] The comparative results show that, compared with the comparative example, after using the formaldehyde-loaded amino-rich mesoporous molecular sieve composite material described in this embodiment for formaldehyde slow release, the selectivity of bispentaerythritol increased from 2.1% in the conventional process of Comparative Example 1 to 9.8-11.2%, an increase of about 4-5 times. This fully verifies the significant effect of the slow-release formaldehyde strategy of this invention in improving the selectivity of bispentaerythritol synthesis; the decrease in pentaerythritol yield is controllable; and the activity of the composite material remains ≥80% after 5 cycles, making it suitable for industrial scale-up.

[0044] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0045] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing dipentaerythritol, characterized in that, Includes the following steps: Step 1: Prepare a composite material comprising an amino-rich mesoporous molecular sieve, an alkaline oxide, and formaldehyde; the amino-rich mesoporous molecular sieve is selected from one of an amino-functionalized hybrid support composed of MCM-41-NH2, UiO-66-NH2, or SBA-15-NH2; the alkaline oxide is one or more of MgO, CaO, and ZnO; the specific preparation steps of the composite material include: mixing the amino-rich mesoporous molecular sieve with the alkaline oxide and adsorbing formaldehyde to obtain the composite material, wherein the amino groups of the amino-rich mesoporous molecular sieve form imine bonds and hemiacetal amine structures with formaldehyde, thereby reversibly loading formaldehyde into the composite material; Step 2: Add acetaldehyde or an acetaldehyde-formaldehyde mixture into the reactor in one step, and then add the composite material obtained in Step 1 into the reactor. Step 3: Add alkali continuously or in batches to the reactor at a controlled rate to generate dipentaerythritol. After the reaction is completed, filter and recover the composite material. Step four: calcine the composite material recovered in step three to regenerate it. Then, impregnate the regenerated composite material with formaldehyde solution again using the method in step one to load it with formaldehyde, and return it to step two for recycling.

2. The method for synthesizing dipentaerythritol according to claim 1, characterized in that, In the composite material of step one, the amount of amino-rich mesoporous molecular sieve added is 60-80% by mass; the amount of alkaline oxide added is 5-15%; and the amount of formaldehyde added is 10-25%.

3. The method for synthesizing dipentaerythritol according to claim 1, characterized in that, In step three, the reaction temperature is 30-50℃ and the alkali addition time is 0.5-3h; in step four, the calcination temperature is 200-300℃ and the calcination time is 0.5-4h.

4. The method for synthesizing dipentaerythritol according to claim 1, characterized in that, The amino-rich mesoporous molecular sieve has a pore size of 2-5 nm and a specific surface area of ​​not less than 500 m² / g.

5. The method for synthesizing dipentaerythritol according to claim 1, characterized in that, The alkali mentioned in step three is NaOH, KOH, or a mixed aqueous solution thereof, and the total amount of alkali added is 0.8-1.5 times the molar amount of acetaldehyde, calculated by the number of moles of OH⁻.

6. A composite material for synthesizing dipentaerythritol, characterized in that, The composite material is prepared using the specific preparation steps of the composite material described in claim 1. By mass percentage, the composite material contains 60-80% amino-rich mesoporous molecular sieve, 5-15% alkaline oxide, and 10-25% formaldehyde.

7. The composite material for synthesizing bispentaerythritol according to claim 6, characterized in that, The composite material has a saturated adsorption capacity of formaldehyde greater than or equal to 0.15 g / g under sealed conditions at 25°C.

8. The composite material for synthesizing bispentaerythritol according to claim 6, characterized in that, The formaldehyde removal rate of the composite material is greater than or equal to 78% after calcination at 250°C for 2 hours.

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