Green process for preparing HDDMA by using magnetic solid acid catalyst

Abstract

The invention relates to the technical field of preparation of HDDMA, and discloses a green process for preparing HDDMA by using a magnetic solid acid catalyst, which comprises the following steps: S1, esterification section: firstly, adding cyclohexane, methacrylic acid, hydroquinone, 1, 6-hexanediol and the magnetic solid acid catalyst into an esterification kettle, and carrying out esterification reaction to obtain an esterification product; s2, a water washing neutralization section: sequentially carrying out water washing, extraction and water washing treatment on the esterification product; s3, a desolventizing section: heating the product subjected to water washing and neutralization to remove the solvent, so as to obtain HDDMA; according to the invention, the preparation process is greatly improved, and an HDDMA preparation system with both high efficiency and green property is constructed. Compared with the traditional process, the catalyst dosage is obviously reduced, the recycling frequency is increased, and the production cost is reduced; the product purity is improved, and the requirements of high-end photocuring materials can be met; the wastewater discharge amount is greatly reduced, acid mist pollution is avoided, and the environment-friendly requirement is met.

Description

Technical Field

[0001] This invention relates to the field of HDDMA preparation technology, specifically a green process for preparing HDDMA using a magnetic solid acid catalyst. Background Technology

[0002] HDDMA (1,6-hexanediol dimethacrylate), as an important functional organic compound, is widely used in coatings, adhesives, plastics, and optoelectronic materials due to its excellent photocuring properties and crosslinking characteristics. Traditional HDDMA preparation processes mainly use liquid acids such as sulfuric acid and phosphoric acid as catalysts, synthesizing HDDMA through the esterification reaction of 1,6-hexanediol and methacrylic acid. However, this type of process has significant technical drawbacks: the low catalytic activity of the liquid acid catalysts leads to long reaction times and frequent side reactions (such as double bond polymerization and product isomerization), resulting in product purity typically only reaching 90-92%; the catalyst forms a homogeneous system with the reaction system, making it difficult to recover using simple physical methods, with a catalyst loss rate exceeding 30% per reaction, resulting in high production costs; and the discharge of large amounts of acidic wastewater causes serious environmental pollution. Statistics show that traditional processes require the discharge of 2-3 tons of acidic wastewater for every ton of HDDMA produced, which does not meet the requirements of green chemical development.

[0003] In the field of esterification process optimization, the development of solid acid catalysts has become a research hotspot, but existing technologies still face key bottlenecks: conventional solid acids (such as molecular sieves and supported sulfonic acids) have low acid center density (≤1.0 mmol / g), and the active sites are easily occupied by hydrated ions in the reaction system, resulting in limited improvement in catalytic efficiency.

[0004] To address the aforementioned issues, this invention proposes a green preparation process based on magnetic solid acid catalysts, achieving a dual breakthrough in catalytic performance and environmental friendliness. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a green process for preparing HDDMA using a magnetic solid acid catalyst.

[0006] The technical solution adopted by this invention to solve its technical problem is: a green process for preparing HDDMA using a magnetic solid acid catalyst, comprising the following steps: S1 Esterification Section: First, cyclohexane, methacrylic acid, hydroquinone, 1,6-hexanediol, and magnetic solid acid catalyst are added to the esterification reactor in the following mass ratio (30-100):(100-400):(2-10):(5-10):(100-500). The esterification reaction is carried out at a temperature ≤104℃ and a pressure of 0.25MPa until the acid value reaches ≤0.8mgKOH / g, and the esterification product is obtained. S2 Water Washing and Neutralization Section: The esterification product is sequentially subjected to water washing, extraction and water washing treatment; S3 Desolventizing Section: The product after water washing and neutralization is heated to remove the solvent and obtain HDDMA.

[0007] As a further technical solution, the preparation method of the magnetic solid acid catalyst includes: Microcrystalline cellulose soaked in 10wt% phosphoric acid solution at 90-95℃ for 2 hours is mixed with ferric chloride at a mass ratio of (0.8-1.2):1, and deionized water is added and stirred to form a slurry; The liquid-to-solid ratio of phosphoric acid solution to microcrystalline cellulose is 5:1; The slurry was heated to evaporate the moisture and then dried. It was then carbonized in a nitrogen atmosphere to obtain a black solid.

[0008] As a further technical solution, the carbonization process employs a segmented gradient heating method: First, raise the temperature to 300-350℃ at 3-5℃ / min and hold for 3-4 hours. Then, raise the temperature to 450-480℃ at 1-2℃ / min and hold for 1-2 hours. Finally, raise the temperature to 600±10℃ at 3-5℃ / min and hold for 12-13 hours.

[0009] As a further technical solution, the black solid is ground into powder and then sulfonated with 98% concentrated sulfuric acid solution at 160-166℃ for 24-25 hours at a ratio of 1g of carbonized product to 20-30mL of sulfuric acid. During sulfonation, aluminum chloride of 0.8-1.4% of the carbonized product mass is added, and finally the mixture is filtered.

[0010] As a further technical solution, after the sulfonation reaction is completed, the filtered product is washed with deionized water until neutral, and then dried at 105°C to constant weight.

[0011] As a further technical solution, the saturation magnetization of the magnetic solid acid catalyst is ≥28.3 emu / g, and the acid density retention rate is ≥90% after 10 cycles of use.

[0012] As a further technical solution, in the water washing and neutralization section, the water washing temperature is 20-25℃, and the amount of water used each time is 1-1.5 times the volume of the esterification product; the extractant is a 1:1 volume ratio ethanol / water mixture, the amount of which is 1-2 times the volume of the esterification product, and ultrasonic extraction is performed at 40-50kHz for 30-40 minutes.

[0013] As a further technical solution, the solvent removal section employs a combination of stepped heating and a vacuum of -0.09 MPa to remove the solvent. The temperature was increased in stages: 60℃, 80℃, and 100℃, with a heating rate of 10℃ / h and a holding time of 30 minutes at each temperature.

[0014] As a further technical solution, the esterification reaction is carried out in a pulsed microwave reactor with a power of 5-5.5kW.

[0015] The beneficial effects of this invention are: This invention improves the catalytic efficiency of magnetic solid acid catalysts through gradient carbonization and hierarchical pore construction. A segmented gradient heating process induces ordered carbonization of microcrystalline cellulose by controlling the pyrolysis rate, forming a three-tiered pore network of micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm). This structure significantly increases the catalyst's specific surface area, providing efficient diffusion channels for substrate molecules, significantly reducing the resistance to reactant transport, and resulting in a marked improvement in catalytic efficiency compared to single-pore structures.

[0016] This invention utilizes carbonization under a nitrogen atmosphere to form nano-sized iron(III) oxide particles, which are uniformly dispersed within a carbon matrix, creating a composite magnetic structure. This structure results in a catalyst saturation magnetization ≥28.3 emu / g, leading to high separation efficiency under an applied magnetic field. The introduction of magnetic particles also optimizes the electron cloud distribution of the acid centers through magnetic moment coupling. Aluminum chloride is added during sulfonation, and a high-temperature sulfonation reaction forms -SO3H and Al groups on the carbon matrix surface. 3+ The synergistic action site. Al 3+ As a Lewis acid center, it forms a dual-acid center catalytic system with the Brønsted acid center (-SO3H): the Brønsted acid promotes the protonation reaction of hydroxyl and carboxyl groups, while the Lewis acid adsorbs the carbonyl oxygen of methacrylic acid through empty orbitals. The two work together to reduce the activation energy of the esterification reaction, significantly shorten the reaction time, and further increase the rate of acid value reduction.

[0017] This invention significantly improves the selectivity of the esterification reaction by limiting the raw material mass ratio and reaction conditions in the esterification stage and combining it with pulsed microwave assistance. Microwave radiation enhances mass transfer through the polar molecular oscillation effect, and combined with the high activity of the magnetic catalyst, the HDDMA yield is ≥92.5%, which is significantly higher than the yield of traditional heating processes.

[0018] In the water washing and neutralization section, ultrasonic-assisted extraction with an ethanol / water mixed solvent is used. The cavitation effect accelerates the dissolution of unreacted raw materials, resulting in high extraction efficiency and significantly shorter extraction time compared to traditional stirring extraction. The water washing temperature is controlled at 20-25℃ to avoid HDDMA hydrolysis, while also reducing energy consumption and significantly lowering wastewater discharge compared to traditional processes.

[0019] The catalyst prepared by this invention exhibits high cycling stability, retaining ≥90% of its acid density and maintaining an HDDMA yield above 88% after 10 cycles. This is primarily due to the hierarchical pore structure reducing carbon buildup and blockage, and the reduction of Al... 3+The synergistic effect with -SO3H enhances the stability of the acid center, and magnetic separation avoids mechanical loss of the catalyst, thus achieving high stability.

[0020] This invention establishes a highly efficient and environmentally friendly HDDMA preparation system through significant improvements in the preparation process. Compared with traditional processes, the amount of catalyst used is significantly reduced, the number of recycling cycles is increased, and production costs are lowered; the purity of the product is improved, meeting the requirements of high-end photocurable materials; wastewater discharge is significantly reduced, and there is no acid mist pollution, complying with environmental protection requirements. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of a green process for preparing HDDMA using a magnetic solid acid catalyst. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a green process for preparing HDDMA using a magnetic solid acid catalyst, comprising the following steps: S1 Ester Chemical Section First, cyclohexane, methacrylic acid, hydroquinone, 1,6-hexanediol, and a magnetic solid acid catalyst are added to an esterification reactor in a mass ratio of (30-100):(100-400):(2-10):(5-10):(100-500). The esterification reaction is carried out at a temperature ≤104℃ and a pressure of 0.25MPa until the acid value reaches ≤0.8mgKOH / g, at which point the esterified product is obtained.

[0024] S2 Water Washing and Neutralization Section The esterified product is subjected to water washing, extraction, and water washing in sequence: the water washing temperature is 20-25℃, and the amount of water used each time is 1-1.5 times the volume of the esterified product; the extractant is a 1:1 volume ratio ethanol / water mixture, and the amount used is 1-2 times the volume of the esterified product, and ultrasonic extraction is performed at 40-50kHz for 30-40 minutes; the final water washing temperature is 20-25℃, and the amount of water used is 0.5-1 times the volume of the esterified product.

[0025] S3 Desolventizing Section The product after water washing and neutralization was subjected to solvent removal by step heating and vacuum of -0.09 MPa: the step heating was 60℃, 80℃ and 100℃ respectively, the heating rate was 10℃ / h, and each temperature was held for 30 min. HDDMA was obtained after solvent removal.

[0026] Preparation method of magnetic solid acid catalyst Pretreatment: Soak microcrystalline cellulose in a 10wt% phosphoric acid solution at 90-95℃ for 2 hours. The liquid-solid ratio of the phosphoric acid solution to the microcrystalline cellulose is 5:1.

[0027] Mixing and pulping: Pretreated microcrystalline cellulose and ferric chloride are mixed at a mass ratio of (0.8-1.2):1, and deionized water is added and stirred to form a uniform slurry.

[0028] Segmented gradient carbonization: After heating and evaporating the moisture from the slurry, the slurry is dried and then carbonized under a nitrogen atmosphere. Specifically, the temperature is first increased to 300-350℃ at 3-5℃ / min and held for 3-4 hours, then increased to 450-480℃ at 1-2℃ / min and held for 1-2 hours, and finally increased to 600±10℃ at 3-5℃ / min and held for 12-13 hours to obtain a black solid.

[0029] Sulfonation modification: After grinding the black solid into powder, it is sulfonated with 98% concentrated sulfuric acid solution at a ratio of 1g of carbonized product to 20-30mL of sulfuric acid at 160-166℃ for 24-25 hours. During sulfonation, aluminum chloride of 0.8-1.4% of the carbonized product mass is added. After the reaction is completed, the mixture is filtered.

[0030] Post-processing: Wash the filtered product with deionized water until neutral, and dry it at 105℃ to constant weight to obtain a magnetic solid acid catalyst with a saturation magnetization ≥28.3 emu / g and an acid density retention rate ≥90% after 10 cycles.

[0031] The following are specific embodiments. Example 1 Catalyst preparation Take 10g of microcrystalline cellulose, add 50mL of 10wt% phosphoric acid solution, and soak at 90℃ for 2 hours.

[0032] The pretreated microcrystalline cellulose was mixed with 8g of ferric chloride, and deionized water was added and stirred to form a slurry. After evaporating the water, the slurry was dried.

[0033] Carbonization under a nitrogen atmosphere: First, the temperature is increased to 300℃ at 3℃ / min and held for 3 hours; then the temperature is increased to 450℃ at 1℃ / min and held for 1 hour; finally, the temperature is increased to 600℃ at 3℃ / min and held for 12 hours to obtain a black solid.

[0034] The black solid was ground and then sulfonated with 200 mL of 98% concentrated sulfuric acid and 0.8 g of aluminum chloride at 160 °C for 24 hours. After filtration, it was washed with deionized water until neutral and dried at 105 °C to constant weight.

[0035] HDDMA preparation The catalyst was fed into an esterification reactor at a mass ratio of cyclohexane:methacrylic acid:hydroquinone:1,6-hexanediol:catalyst = 30:100:2:5:100, and reacted at 100℃ and 0.25MPa until the acid value reached 0.75mgKOH / g.

[0036] Water washing and neutralization: First, use 100 mL of 20°C water and 100 mL of ethanol / water mixture (1:1) for extraction. Sonicate at 40 kHz for 30 minutes, then wash with 50 mL of 20°C water.

[0037] Desolventizing section: The temperature is increased in stages to 60℃, 80℃, and 100℃, and each temperature is held for 30 minutes. The vacuum degree is -0.09MPa to obtain HDDMA.

[0038] Example 2 Catalyst preparation Pretreatment: Take 12g of microcrystalline cellulose, add 60mL of 10wt% phosphoric acid solution, and soak at 95℃ for 2 hours.

[0039] Mixed pulping: The pretreated microcrystalline cellulose is mixed with 12g of ferric chloride, deionized water is added and stirred to form a uniform pulp, which is then heated to evaporate the water and dried.

[0040] Segmented gradient carbonization: Under a nitrogen atmosphere, the temperature is first increased to 350℃ at a heating rate of 5℃ / min and held for 4 hours; then increased to 480℃ at a heating rate of 2℃ / min and held for 2 hours; finally increased to 590℃ at a heating rate of 5℃ / min and held for 13 hours to obtain a black solid.

[0041] Sulfonation modification: The black solid was ground into powder and sulfonated with 300 mL of 98% concentrated sulfuric acid and 0.168 g of aluminum chloride (accounting for 1.4% of the mass of the carbonization product) at 166 °C for 25 hours. After the reaction was completed, the mixture was filtered.

[0042] Post-processing: Wash the filtered product with deionized water until neutral, and dry at 105°C to constant weight.

[0043] HDDMA preparation Esterification stage: Cyclohexane: methacrylic acid: hydroquinone: 1,6-hexanediol: catalyst = 100:400:10:10:500 were added to the esterification reactor and reacted at 104℃ and 0.25MPa until the acid value reached 0.8mgKOH / g, yielding the esterified product.

[0044] Water washing and neutralization section: First wash: temperature 25℃, water volume 200mL (1.5 times the volume of esterified product). Extraction: Use 200 mL of ethanol / water mixture with a volume ratio of 1:1 and sonicate at 50 kHz for 40 minutes. Second wash: temperature 25℃, water volume 100mL (1 times the volume of esterification product).

[0045] Solvent removal section: The solvent is removed by stepwise heating (60℃, 0℃, 100℃, heating rate 10℃ / h, holding for 30min each) and vacuum degree -0.09MPa to obtain HDDMA.

[0046] Example 3 Catalyst preparation Pretreatment: Take 11g of microcrystalline cellulose, add 55mL of 10wt% phosphoric acid solution, and soak at 93℃ for 2 hours.

[0047] Mixed pulping: The pretreated microcrystalline cellulose is mixed with 10g of ferric chloride, deionized water is added and stirred to form a uniform pulp, which is then heated to evaporate the water and dried.

[0048] Segmented gradient carbonization: Under a nitrogen atmosphere, the temperature was first increased to 320℃ at a heating rate of 4℃ / min and held for 3.5 hours; then increased to 460℃ at a heating rate of 1.5℃ / min and held for 1.5 hours; finally increased to 610℃ at a heating rate of 4℃ / min and held for 12.5 hours to obtain a black solid.

[0049] Sulfonation modification: The black solid was ground into powder and sulfonated with 250 mL of 98% concentrated sulfuric acid and 0.121 g of aluminum chloride (accounting for 1.1% of the mass of the carbonization product) at 163 °C for 24.5 hours. After the reaction was completed, the mixture was filtered.

[0050] Post-processing: Wash the filtered product with deionized water until neutral, and dry at 105°C to constant weight.

[0051] HDDMA preparation Esterification stage: Cyclohexane: methacrylic acid: hydroquinone: 1,6-hexanediol: catalyst = 60:200:6:7:300 were added to the esterification reactor and reacted at 102℃ and 0.25MPa until the acid value reached 0.78mgKOH / g, yielding the esterified product.

[0052] Water washing and neutralization section: First wash: temperature 22℃, water volume 150mL (1.2 times the volume of esterified product). Extraction: Use 150 mL of ethanol / water mixture with a volume ratio of 1:1 and sonicate at 45 kHz for 35 minutes. Second wash: temperature 22℃, water volume 75mL (0.6 times the volume of esterification product).

[0053] Solvent removal section: The solvent is removed by stepwise heating (60℃, 0℃, 100℃, heating rate 10℃ / h, holding for 30min each) and vacuum degree -0.09MPa to obtain HDDMA.

[0054] Example 4 Catalyst preparation Pretreatment: Take 9g of microcrystalline cellulose, add 45mL of 10wt% phosphoric acid solution, and soak at 92℃ for 2 hours.

[0055] Mixing and pulping: Mix the pretreated microcrystalline cellulose with 9g of ferric chloride, add deionized water and stir to form a uniform slurry, heat to evaporate the water and then dry.

[0056] Segmented gradient carbonization: Under a nitrogen atmosphere, the temperature was first increased to 330℃ at a heating rate of 4℃ / min and held for 3.5 hours; then increased to 470℃ at a heating rate of 1.5℃ / min and held for 1.5 hours; finally increased to 600℃ at a heating rate of 4℃ / min and held for 12 hours to obtain a black solid.

[0057] Sulfonation modification: The black solid was ground into powder and sulfonated with 225 mL of 98% concentrated sulfuric acid and 0.108 g of aluminum chloride (accounting for 1.2% of the mass of the carbonization product) at 165 °C for 24.5 hours. After the reaction was completed, the mixture was filtered.

[0058] Post-processing: Wash the filtered product with deionized water until neutral, and dry at 105°C to constant weight.

[0059] HDDMA preparation Esterification stage: Cyclohexane: methacrylic acid: hydroquinone: 1,6-hexanediol: catalyst = 70:250:7:8:350 were added to the esterification reactor and reacted at 103℃ and 0.25MPa until the acid value reached 0.76mgKOH / g, yielding the esterified product.

[0060] Water washing and neutralization section: First wash: temperature 23℃, water volume 130mL (1.3 times the volume of esterified product). Extraction: Use 130 mL of ethanol / water mixture with a volume ratio of 1:1 and sonicate at 48 kHz for 38 minutes. Second wash: temperature 23℃, water volume 65mL (0.65 times the volume of esterification product).

[0061] Solvent removal section: The solvent is removed by stepwise heating (60℃, 80℃, 100℃, heating rate 10℃ / h, holding for 30min each) and vacuum degree -0.09MPa to obtain HDDMA.

[0062] Example 5 Catalyst preparation Pretreatment: Take 10.5g of microcrystalline cellulose, add 52.5mL of 10wt% phosphoric acid solution, and soak at 94℃ for 2 hours.

[0063] Mixed pulping: The pretreated microcrystalline cellulose is mixed with 10.5g of ferric chloride, deionized water is added and stirred into a pulp, the water is evaporated and then dried.

[0064] Segmented gradient carbonization: Under a nitrogen atmosphere, the temperature is first increased to 350℃ at 5℃ / min and held for 4 hours; then increased to 480℃ at 2℃ / min and held for 2 hours; finally, the temperature is increased to 590℃ at 5℃ / min and held for 13 hours to obtain a black solid.

[0065] Sulfonation modification: The black solid was ground and then sulfonated with 294 mL of 98% concentrated sulfuric acid and 0.147 g of aluminum chloride (accounting for 1.4% of the mass of the carbonization product) at 166 °C for 25 hours, and then filtered.

[0066] Post-treatment: Wash with deionized water until neutral, and dry at 105°C to constant weight.

[0067] HDDMA preparation Esterification stage: The catalyst was fed in a mass ratio of cyclohexane:methacrylic acid:hydroquinone:1,6-hexanediol:catalyst = 60:180:5:7:250 and reacted at 102℃ and 0.25MPa until the acid value reached 0.77mgKOH / g, yielding the esterified product.

[0068] Water washing and neutralization section: First wash: temperature 24℃, water volume 140mL (1.4 times the volume of esterified product). Extraction: Use 140 mL of ethanol / water mixture (1:1 v / v) and sonicate at 49 kHz for 39 minutes. Second wash: temperature 24℃, water volume 70mL (0.7 times the volume of esterified product).

[0069] Solvent removal process: Under the same step temperature and vacuum conditions as in Example 1, HDDMA is obtained after solvent removal.

[0070] The following is a comparative example Comparative Example 1 Catalyst preparation The segmented gradient heating is omitted, and the temperature is directly increased to 600℃ at 10℃ / min, and held for 12 hours. The remaining steps are the same as in Example 1.

[0071] HDDMA preparation The raw material ratio and process conditions are the same as in Example 1. The reaction is carried out until the acid value is 0.8 mg KOH / g, and the water washing and desolvation steps remain unchanged.

[0072] Comparative Example 2 Catalyst preparation Aluminum chloride is not added during sulfonation, and the remaining steps are the same as in Example 1.

[0073] HDDMA preparation The raw material ratio and process conditions are the same as in Example 1, and the subsequent processing steps remain unchanged.

[0074] Comparative Example 3 Catalyst preparation Instead of using a magnetic solid acid catalyst, sulfuric acid (5% of the mass of methacrylic acid) is used.

[0075] HDDMA preparation The raw materials were the same as in Example 1, and the reaction was carried out at 100°C and 0.25 MPa until the acid value reached 0.8 mg KOH / g.

[0076] The water washing and neutralization section uses traditional stirring extraction (without ultrasonic assistance), with the same amount of extractant as in Example 1, stirring speed of 60 r / min, and extraction time of 60 minutes.

[0077] The solvent removal process is the same as in Example 1.

[0078] test Magnetic solid acid catalyst saturation magnetization test Referring to GB / T13560-2017 "Sintered NdFeB Permanent Magnet Materials", the saturation magnetization of the catalyst was determined using a vibrating sample magnetometer (VSM). The catalyst samples from the examples and comparative examples were ground into fine powder, placed in a sample holder, and subjected to a magnetic field of 0-1.5T at room temperature. The hysteresis loops were recorded to determine the saturation magnetization values. The results are as follows: Table 1

[0079] As shown in Table 1, the saturation magnetization of the catalysts in Examples 1-5 was ≥28.3 emu / g. In Comparative Example 1, the lack of segmented gradient heating resulted in uneven distribution of magnetic particles during carbonization, leading to a significant decrease in magnetization. Comparative Example 2 did not include aluminum chloride, affecting the formation of the magnetic phase. Comparative Example 3 used a conventional liquid acid, which is non-magnetic and cannot be recovered. Segmented gradient heating and the addition of aluminum chloride are crucial for enhancing the magnetic properties of the catalysts.

[0080] HDDMA yield test HDDMA yield calculation formula: Yield (%) = (Actual HDDMA mass obtained / Theoretical HDDMA mass) × 100%. The theoretical mass is calculated based on the molar amount of 1,6-hexanediol, assuming complete esterification. HDDMA content was quantitatively analyzed using gas chromatography (GC). Chromatographic conditions: HP-5 column, column temperature 180℃, injection port temperature 250℃, detector temperature 280℃, nitrogen carrier gas. Results are as follows: Table 2

[0081] As shown in Table 2, the yields of the examples were all above 92%, while the yields of the comparative examples were significantly lower. The lack of staged heating in Comparative Example 1 resulted in insufficient active sites on the catalyst, leading to incomplete esterification. Comparative Example 2 lacked aluminum chloride, reducing the number of acid centers and decreasing catalytic efficiency. Comparative Example 3 had poor selectivity in its liquid acid catalyst, resulting in numerous side reactions and the lowest yield. The catalyst preparation process of this invention effectively improves the esterification reaction efficiency.

[0082] Catalyst efficiency test Catalytic efficiency is expressed as the decrease in acid value per unit time (mgKOH / g·h). During the esterification reaction, samples were taken every hour to measure the acid value, and the average rate of decrease in acid value was calculated. Acid value determination was performed according to GB / T1668-2008 "Determination of Acid Value and Acidity of Plasticizers" using acid-base titration. The results are as follows: Table 3

[0083] As shown in Table 3, the catalytic efficiency of the examples is significantly higher than that of the comparative examples. The catalyst in Comparative Example 1 has insufficient active surface area due to defects in the carbonization process; the acid center synergistic effect of Comparative Example 2 is lacking, resulting in a reduced catalytic rate; although the liquid acid catalyst in Comparative Example 3 has a high initial efficiency, it is easily deactivated and has poor selectivity. This invention constructs a highly efficient acid center structure and improves catalytic efficiency by staged heating and doping with aluminum chloride and iron oxide.

[0084] Catalyst recycling performance test The catalyst was repeatedly used in the HDDMA preparation reaction. After each reaction, the catalyst was recovered using an external magnetic field, washed with water, dried, and reused. The retention rate of acid density of the catalyst and the change in HDDMA yield were tested after 10 cycles. The acid density was determined using the NH3-TPD method, referring to GB / T23659-2009 "Determination of Acid Value of Catalysts". The results are as follows: Table 4

[0085] As shown in Table 1, the catalysts in the examples maintained an acid density retention rate of ≥90% and an HDDMA yield of over 88% after 10 cycles, demonstrating good cycle stability. Comparative Examples 1 and 2, due to poor catalyst structural stability, experienced significant acid center loss during recycling; Comparative Example 3 could not be recovered and therefore could not be recycled. The catalyst preparation process of this invention effectively improves the catalyst's cycle life and reduces production costs.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A green process for preparing HDDMA using a magnetic solid acid catalyst, characterized in that, Includes the following steps: S1 Esterification Section: First, cyclohexane, methacrylic acid, hydroquinone, 1,6-hexanediol, and magnetic solid acid catalyst are added to the esterification reactor in the following mass ratio (30-100):(100-400):(2-10):(5-10):(100-500). The esterification reaction is carried out at a temperature ≤104℃ and a pressure of 0.25MPa until the acid value reaches ≤0.8mgKOH / g, and the esterification product is obtained. S2 Water Washing and Neutralization Section: The esterification product is sequentially subjected to water washing, extraction and water washing treatment; S3 Desolventizing Section: The product after water washing and neutralization is heated to remove the solvent and obtain HDDMA.

2. The green process according to claim 1, characterized in that, The preparation method of the magnetic solid acid catalyst includes: Microcrystalline cellulose soaked in 10wt% phosphoric acid solution at 90-95℃ for 2 hours is mixed with ferric chloride at a mass ratio of (0.8-1.2):1, and deionized water is added and stirred to form a slurry; The liquid-to-solid ratio of phosphoric acid solution to microcrystalline cellulose is 5:1; The slurry was heated to evaporate the moisture and then dried. It was then carbonized in a nitrogen atmosphere to obtain a black solid.

3. The green process according to claim 2, characterized in that, The carbonization process employs a segmented gradient heating method: First, raise the temperature to 300-350℃ at 3-5℃ / min and hold for 3-4 hours. Then, raise the temperature to 450-480℃ at 1-2℃ / min and hold for 1-2 hours. Finally, raise the temperature to 600±10℃ at 3-5℃ / min and hold for 12-13 hours.

4. The green process according to claim 3, characterized in that, After grinding the black solid into powder, it is sulfonated with 98% concentrated sulfuric acid solution at a ratio of 1g of carbonized product to 20-30mL of sulfuric acid at 160-166℃ for 24-25 hours. During sulfonation, aluminum chloride of 0.8-1.4% of the carbonized product mass is added. Finally, the mixture is filtered.

5. The green process according to claim 4, characterized in that, After the sulfonation reaction is completed, the filtered product is washed with deionized water until neutral and dried at 105°C to constant weight.

6. The green process according to claim 5, characterized in that, The magnetic solid acid catalyst has a saturation magnetization of ≥28.3 emu / g and an acid density retention rate of ≥90% after 10 cycles of use.

7. The green process according to claim 1, characterized in that, In the water washing and neutralization section, the water washing temperature is 20-25℃, and the amount of water used each time is 1-1.5 times the volume of the esterification product; the extractant is a 1:1 volume ratio ethanol / water mixture, and the amount used is 1-2 times the volume of the esterification product, and ultrasonic extraction is performed at 40-50kHz for 30-40 minutes.

8. The green process according to claim 1, characterized in that, The solvent removal process employs a combination of stepped temperature increase and a vacuum of -0.09 MPa to remove the solvent. The temperature was increased in stages: 60℃, 80℃, and 100℃, with a heating rate of 10℃ / h and a holding time of 30 minutes at each temperature.

9. The green process according to claim 1, characterized in that, The esterification reaction is carried out in a pulsed microwave reactor with a power of 5-5.5 kW.

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