A process for the synthesis of 2,2,4-trimethyl-1,3-pentanediol dibenzoate

Abstract

This invention belongs to the field of chemical synthesis and polymer material additives technology, specifically relating to a synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate. It includes the following steps: Step (1) Step-by-step esterification reaction: 2,2,4-trimethyl-1,3-pentanediol is mixed with benzoic acid, a composite catalyst is added, and a step-by-step esterification dehydration reaction is carried out under heating conditions to obtain a crude ester reaction solution; Step (2) Neutralization and washing; Step (3) Light removal and viscosity reduction / flow-promoting molecular distillation purification: An anti-yellowing agent is added to the organic phase after washing in step (2), and light removal is carried out under reduced pressure at 100–130℃ and 1000–5000 Pa absolute pressure to remove the water-carrying agent and water; subsequently, the crude product is continuously pumped into a scraped-film molecular distillation apparatus for high-vacuum purification, controlling the evaporator heating surface temperature at 150–200℃ and the system absolute vacuum at 10–200 Pa. This invention provides a synthesis and purification process for TMPD dibenzoate with high diester content and low hue.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis and polymer material additives technology, specifically relating to a synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate. Background Technology

[0002] 2,2,4-Trimethyl-1,3-pentanediol dibenzoate (TMPD dibenzoate) is an environmentally friendly non-phthalic plasticizer. Due to the significant steric hindrance of the secondary hydroxyl group at the C3 position in the TMPD molecule, although the total ester content in some industrial-grade products may meet the standards, the proportion of diester is usually around 90% to 91%, which affects some of its physical properties.

[0003] Traditional direct esterification methods typically require strong acids and prolonged reactions at high temperatures (e.g., 190-200°C) to overcome steric hindrance. However, under high temperature and strong Lewis acid conditions, ligand alcohol molecules detached from the catalyst (e.g., titanate ester) readily undergo transesterification with benzoic acid, generating a complex mixture of ester byproducts that are difficult to separate. Simultaneously, high temperatures can also lead to the dehydration and rearrangement of TMPD to form olefins, causing a darkening of the color of the ester products. Furthermore, the target product exhibits a high kinetic viscosity (approximately 630 mPa·s) at room temperature (25°C). In conventional molecular distillation purification processes using ambient temperature cooling water, vaporized high-viscosity esters, upon contact with a low-temperature condensing surface, tend to form a liquid film with poor fluidity, which may cause liquid film accumulation or even affect vacuum stability. On the other hand, if the initial feed contains a large amount of residual moisture, flash boiling is likely to occur under extremely high vacuum, which not only disrupts the uniformity of the liquid film distribution, but also causes mechanical entrainment from splashed droplets, allowing heavy component impurities to cross the evaporation surface and enter the light component distillation tank. At the same time, a large influx of water vapor can cause the pump vacuum to collapse instantaneously, resulting in a decrease in the quality of the final product. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a synthesis process for 2,2,4-trimethyl-1,3-pentanediol dibenzoate, and to provide a synthesis and purification process for TMPD dibenzoate with high diester ratio and low hue.

[0005] This invention adopts the following technical solution: a process for synthesizing 2,2,4-trimethyl-1,3-pentanediol dibenzoate, comprising the following steps: Step (1) Stepwise esterification reaction: 2,2,4-trimethyl-1,3-pentanediol and benzoic acid are mixed, a composite catalyst is added, and a stepwise esterification dehydration reaction is carried out under heating conditions to obtain a crude ester reaction solution; wherein, the composite catalyst is a mixture of organotitanium compounds and organotin compounds, and the molar ratio of organotitanium compounds to organotin compounds is 1:0.5 to 1:3; the stepwise esterification dehydration reaction includes the following two controlled stages: the first stage reaction: the temperature of the reactants is controlled at 130 to 150 ℃, and the reaction is kept at a low pressure of less than 0.15 MPa for 1 to 3 hours. After the heat preservation is completed, the pressure is released to remove some of the small molecule alcohol ligands dissociated from the composite catalyst from the system; the second stage reaction: an azeotropic dehydrating agent is added, the system is heated to 160 to 175 ℃, and the reaction is carried out continuously for 4 to 8 hours under the condition that the absolute pressure of the system is reduced to 10 to 40 kPa; Step (2) Neutralization and washing: After the reaction is completed, the crude ester reaction solution is cooled down, and an alkaline aqueous solution is added for neutralization and washing. After separating the aqueous phase, the organic phase is washed with water until neutral. Step (3) Light removal and viscosity reduction via flow-promoting molecular distillation purification: An anti-yellowing agent is added to the organic phase after washing in step (2), and light removal is carried out under reduced pressure at 100-130 ℃ and 1000-5000 Pa absolute pressure to remove water-carrying agent and water; then the crude product is continuously pumped into a scraped film molecular distillation apparatus for high vacuum purification, and the temperature of the heating surface of the evaporator is controlled at 150-200 ℃, and the absolute vacuum of the system is 10-200 Pa; in order to alleviate the accumulation of liquid film caused by the high viscosity of the target product at room temperature, the temperature of the built-in condenser surface of the scraped film molecular distillation apparatus is controlled at 65-85 ℃; the target product 2,2,4-trimethyl-1,3-pentanediol dibenzoate is vaporized and liquefied on the built-in condenser surface and collected as distillate, while heavy component impurities are discharged from the bottom of the equipment.

[0006] Further, the amount of the composite catalyst added is 0.05% to 0.3% of the total mass of the reactants; the organotitanium compound is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, or tetraisobutyl titanate; the organotin compound is selected from one or more of dibutyltin oxide, dibutyltin dilaurate, or stannous isooctanoate.

[0007] Further, the initial molar ratio of 2,2,4-trimethyl-1,3-pentanediol to benzoic acid is 1:2.02 to 1:2.15; the azeotropic dehydrating agent is selected from one or more of toluene, xylene, or n-butyl ether.

[0008] Furthermore, the anti-yellowing agent is selected from pentaerythritol di(2,4-di-tert-butylphenyl) phosphite or phenyl diisodecyl phosphite.

[0009] Furthermore, in step (2), after cooling to 60-70 °C, a 5%-10% sodium carbonate or sodium bicarbonate aqueous solution is added for neutralization.

[0010] Furthermore, the operating parameters of the scraped-film molecular distillation apparatus in step (3) are as follows: the feed throughput of the material is controlled at 5–20 L / (m²). 2 (h), the speed of the built-in rotor of the equipment is controlled at 200-400 r / min, so that the average residence time of the material on the heated surface does not exceed 60 seconds.

[0011] Furthermore, in the first stage of the reaction in step (1), the pressure of the reaction system is controlled from atmospheric pressure to a slightly pressurized state of less than 0.15 MPa to reduce the volatilization loss of 2,2,4-trimethyl-1,3-pentanediol in the initial stage of heating and improve its initial monoesterification conversion rate.

[0012] Furthermore, in the decompression step of step (3), the dehydration endpoint is controlled so that the water content in the organic phase of the crude product is reduced to below 0.10%; in order to reduce the probability of flash boiling when the crude product containing free water enters the 10-200 Pa scraped membrane molecular distillation apparatus, thereby effectively preventing heavy component impurities at the bottom from splashing onto the built-in condenser surface and affecting the quality of the target product.

[0013] A second aspect of the present invention provides a 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared by the above method, wherein the 2,2,4-trimethyl-1,3-pentanediol dibenzoate is a pale yellow to colorless transparent liquid with a water content ≤ 0.10%, a total ester purity ≥ 96.0% by gas chromatography, wherein the diester content is between 92.5% and 95.0%, the acid value is ≤ 0.05 mg KOH / g, and the platinum-cobalt color (Pt-Co) is between 40 and 55.

[0014] The beneficial effects of this invention are: 1. This invention employs an organotitanium-organotin composite synergistic catalytic system, utilizing the synergistic effect of titanium and tin atoms to reduce the reaction activation energy, effectively overcoming the huge steric hindrance of the secondary hydroxyl group of TMPD, thus significantly increasing the proportion of diester.

[0015] 2. The innovative 'pressure-limited primary ester - pressure-limited deep extraction' stepwise process of this invention suppresses the volatilization of raw materials under micro-pressure in the first stage, and combines precise temperature control with negative pressure in the second stage to avoid ester exchange side reactions and dehydration rearrangement caused by high temperature, thus ensuring the high purity and low color of the crude product.

[0016] 3. Addressing the physical challenge of high kinetic viscosity at room temperature in TMPD benzoate, this invention innovatively controls the internal condenser surface temperature of the scraped-film molecular distillation process between 65 and 85 °C. Based on the viscosity-temperature curve characteristics of this ester, within this specific temperature range, the fluid viscosity exhibits an exponential decrease (far below the high viscosity state at room temperature), thus completely resolving the issues of liquid film accumulation and scraped-film rotor obstruction caused by conventional cold water cooling, forming a tight logical closed loop. Furthermore, strictly controlling the feed moisture content below 0.10% completely solves the problems of high-viscosity liquid film accumulation and boiling splashing caused by conventional cooling water, achieving extreme product purification. Attached Figure Description

[0017] Figure 1 GC chromatogram of 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared in Example 1; Figure 2 Color comparison diagrams of 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared in Examples 1 and 2 and Comparative Examples 3 and 4; Figure 3 Color comparison diagrams of 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared in Examples 3, 4 and Comparative Examples 3-5. Detailed Implementation

[0018] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0019] This invention provides a process for synthesizing 2,2,4-trimethyl-1,3-pentanediol dibenzoate, comprising the following steps: Step (1) Stepwise esterification reaction: 2,2,4-trimethyl-1,3-pentanediol and benzoic acid are mixed, a composite catalyst is added, and a stepwise esterification dehydration reaction is carried out under heating conditions to obtain a crude ester reaction solution; wherein, the composite catalyst is a mixture of organotitanium compounds and organotin compounds, and the molar ratio of organotitanium compounds to organotin compounds is 1:0.5 to 1:3. Preferably, the amount of the composite catalyst added is 0.05% to 0.3% of the total mass of the reactants; the organotitanium compound is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, or tetraisobutyl titanate; the organotin compound is selected from one or more of dibutyltin oxide, dibutyltin dilaurate, or stannous isooctanoate; the stepwise esterification dehydration reaction includes the following two controlled stages: the first stage reaction: the temperature of the reactants is controlled at 130-150 °C, and the reaction is kept at a slightly pressurized and sealed state at atmospheric pressure to less than 0.15 MPa for 1-3 hours. After the heat preservation is completed, the pressure is released to allow the primary hydroxyl group of 2,2,4-trimethyl-1,3-pentanediol to preferentially undergo monoesterification, and some of the small molecule alcohol ligands dissociated from the composite catalyst are discharged from the system; the second stage reaction: an azeotropic dehydrating agent is added, the system temperature is raised to 160-175 °C, and the reaction is continuously carried out for 4-8 hours under a negative pressure condition of 10-40 kPa. Within hours, the secondary hydroxyl group with greater steric hindrance undergoes secondary esterification; the initial molar ratio of 2,2,4-trimethyl-1,3-pentanediol to benzoic acid is 1:2.02 to 1:2.15; the azeotropic dehydrating agent is selected from one or more of toluene, xylene, or n-butyl ether.

[0020] Step (2) Neutralization and washing: After the reaction is complete, the crude ester reaction solution is cooled down, and an alkaline aqueous solution is added for neutralization and washing. After separating the aqueous phase, the organic phase is washed with water until neutral. Preferably, after cooling to 60-70 °C, a 5%-10% sodium carbonate or sodium bicarbonate aqueous solution is added for neutralization.

[0021] Step (3) Light removal and viscosity reduction via flow-promoting molecular distillation purification: Add an anti-yellowing agent to the organic phase after washing in step (2), and remove light components under reduced pressure at 100-130 ℃ and 1000-5000 Pa absolute pressure to remove water-carrying agents and water (control the dehydration endpoint so that the water mass fraction in the crude organic phase is reduced to below 0.10%). Then, continuously pump the crude product into a scraped-film molecular distillation apparatus for high-vacuum purification, control the evaporator heating surface temperature at 150-200 ℃, and the system absolute vacuum at 10-200 Pa. To alleviate the accumulation of liquid film caused by the high viscosity of the target product at room temperature, the internal condenser surface temperature of the scraped-film molecular distillation apparatus is controlled at 65-85 ℃. After vaporizing the target product 2,2,4-trimethyl-1,3-pentanediol dibenzoate, liquefy it on the internal condenser surface and collect it as distillate, while discharging heavy component impurities from the bottom of the equipment. Preferably, the operating parameters of the scraped-film molecular distillation apparatus are: the feed throughput of the material is controlled at 5–20 L / (m²). 2 The internal rotor speed of the equipment is controlled at 200-400 r / min, so that the average residence time of the material on the heated surface does not exceed 60 seconds. The anti-yellowing agent is selected from pentaerythritol di(2,4-di-tert-butylphenyl) phosphite or phenyl diisodecyl phosphite.

[0022] The innovative aspects of this invention include: First, an organotitanium-organotin composite synergistic catalytic system was adopted. Single titanate or organotin catalysts have limited efficiency in overcoming the steric hindrance of the secondary hydroxyl group in TMPD due to their coordination configuration and catalytic activity. Combining the two in a specific ratio utilizes the synergistic effect of titanium and tin atoms to lower the reaction activation energy, helping to overcome the esterification barrier and effectively increasing the proportion of diester in the product.

[0023] Second, a process design of "pressure-limited primary esterification - temperature-limited deep extraction" was adopted. In the first stage of esterification, a slight positive pressure (less than 0.15 MPa) was applied under specific conditions to reduce the volatilization of reactants and to preferentially carry out the monoesterification of primary hydroxyl groups. In the second stage, by controlling the maximum temperature at 160-175 ℃, the occurrence of high-temperature transesterification side reactions was reduced, while a negative pressure of 10-40 kPa was introduced to drive the secondary esterification.

[0024] Third, the invention introduces "moisture control, anti-boiling-out, and viscosity-reducing molecular distillation separation technology." After the reaction washing, the dehydration endpoint is controlled during the reduced pressure removal stage, ensuring that the moisture content of the material entering the molecular evaporator is ≤0.10%, reducing the risk of mechanical impurity splashing and contamination caused by high-vacuum boiling. Simultaneously, considering the high viscosity of the target product at room temperature, the invention controls the internal condenser surface temperature of the molecular distillation at 65-85 ℃. Under extremely high vacuum (10-200 Pa), the diester-rich target product is liquefied as a vapor on the condenser surface. The reduced fluid viscosity at this temperature allows it to flow down rapidly as smooth droplets, solving the problem of adhesion and clogging. Meanwhile, heavy components such as polymers with extremely dark color, tar, and catalyst residues are removed from the bottom of the vessel as dead matter, achieving product purification and decolorization.

[0025] Example 1 (1) Stepwise esterification reaction: In a 1000 mL four-necked reactor equipped with a mechanical stirrer, water separator, condenser, and temperature-controlled vacuum device, 146.2 g (1.0 mol) of 2,2,4-trimethyl-1,3-pentanediol (TMPD) and 256.4 g (2.10 mol) of benzoic acid were added sequentially and accurately. Subsequently, a composite catalyst was added: 0.15 g of tetraisopropyl titanate (approximately 0.0005 mol) and 0.45 g of stannous isooctanoate (approximately 0.0011 mol, with an organotitanium to tin molar ratio of approximately 1:2). The total amount of catalyst added was approximately 0.15% of the total mass of the reactants.

[0026] Stirring was started, and the pressure was gradually increased to a slightly positive pressure of approximately 0.12 MPa in a closed system. The temperature was then raised to 140 °C for the first stage reaction. The reaction was held at this temperature for 2 hours to allow the primary hydroxyl groups to preferentially esterify. The slightly pressurized state effectively suppressed excessive volatilization of TMPD. After the holding period, the pressure was released, and some of the isopropanol molecules released from the decomposition of the titanate were distilled off the system. Then, 25 mL of toluene was added as an azeotropic dehydrating agent, and the temperature was slowly raised to 170 °C. The system vacuum pump was then turned on to gradually reduce the pressure to a negative pressure of 30 kPa. The reaction was continued at this temperature and pressure for 5 hours, with water continuously removed using a water separator until no significant water formation was observed, at which point heating was stopped.

[0027] (2) Neutralization and washing: After the reaction solution cools to 65 ℃, add 150 mL of 5% sodium carbonate aqueous solution for neutralization and washing, stir for 30 minutes, let stand and separate the layers, and remove the lower aqueous phase. The remaining organic phase is then washed twice with 60 ℃ warm water until the aqueous phase is neutral.

[0028] (3) Light content removal and viscosity reduction by scraped-film molecular distillation: 0.4 g of pentaerythritol di(2,4-di-tert-butylphenyl)phosphite was added to the washed organic phase as an anti-yellowing agent. After mixing evenly, the mixture was transferred to a vacuum distillation vessel and subjected to vacuum distillation at 110 °C and 2000 Pa absolute pressure to remove the carrying agent toluene and residual moisture for 1.5 hours. Moisture content analysis confirmed that the moisture content of the crude organic phase before entering the scraped-film molecular distillation apparatus had decreased to 0.08%.

[0029] The crude ester was continuously pumped into an effective evaporation area of ​​0.1 m². 2 In a scraped-film molecular evaporator, the system settings are as follows: heat transfer oil heating surface temperature 170 ℃, absolute vacuum degree 50 Pa, feed rate set to 1.0 L / H (equivalent to a feed throughput of 10 L / (m²)). 2 The scraper rotor speed is controlled at 300 r / min, and the material residence time is approximately 40 seconds. The circulating water temperature of the built-in condenser is set to 70 ℃. After the target product rapidly vaporizes on the heating surface, it liquefies on the built-in condenser surface at 70 ℃ and drips smoothly as a liquid with good flowability, which is collected as distillate into the finished product tank.

[0030] Results: The reaction and purification process was stable, with a total yield of 95.5% (approximately 338.5 g of the target product collected). GC analysis showed that the GC conditions were as follows: Detector type: Flame ionization detector (FID); Chromatographic column: AP.SE-30 capillary column (30 m x 0.32 mm x 0.5 μm); Inlet temperature: 260℃; Detector temperature: 280℃; The temperature program conditions were as follows: initial temperature 100℃ (hold for 1 min), then increase to 280℃ at a rate of 20℃ / min (hold for 5 min). Carrier gas: high-purity helium or nitrogen.

[0031] like Figure 1 As shown, The total ester purity was 97.19% (retention times 8.782 and 9.217 represent monoester content). The diester content is 94.88% (retention time is 14.378); the product is a pale yellow transparent liquid without visible mechanical impurities, with an acid value of 0.03 mg KOH / g, a moisture content of 0.05%, and a platinum-cobalt color (Pt-Co) of 42.

[0032] Example 2 (1) Stepwise esterification reaction: 146.2 g (1.0 mol) TMPD and 250.3 g (2.05 mol) benzoic acid were added to a 1000 mL reactor. Composite catalysts were added: 0.17 g tetrabutyl titanate (approximately 0.0005 mol) and 0.37 g dibutyltin oxide (approximately 0.0015 mol, with an organotitanium to tin molar ratio of approximately 1:3), with an addition amount of approximately 0.13%. First stage: Under closed pressure to 0.14 MPa, the reaction was carried out at 130 ℃ for 3 hours; after depressurization and venting, the reaction proceeded to the second stage: 30 mL of n-butyl ether was added as a dehydrating agent, the temperature was raised to 160 ℃, the system pressure was reduced to 40 kPa, and the reaction was carried out continuously for 8 hours.

[0033] (2) Neutralization wash: Cool to 60 °C, neutralize with 150 mL of 8% sodium bicarbonate aqueous solution, and then wash with 60 °C water until neutral.

[0034] (3) Light content removal and viscosity reduction by scraped-film molecular distillation: After adding 0.3 g of phenyl diisodecyl phosphite as an anti-yellowing agent, light content removal was performed at 100 ℃ and 5000 Pa for 2 hours. The moisture content was found to be 0.09%. 0.1 m... 2 A scraped-film molecular evaporator, with the heating surface temperature controlled at 150 ℃, a system vacuum of 200 Pa, and a feed rate of 0.5 L / H (equivalent to a flux of 5 L / (m²)). 2 •h), rotation speed 200r / min. Built-in condenser temperature set to 65℃.

[0035] Results: The product flowed out smoothly with a yield of 93.8%, a total ester purity of 96.6% (including 93.5% diester), no visible mechanical impurities, a moisture content of 0.06%, an acid value of 0.04 mg KOH / g, and a platinum-cobalt color of 45.

[0036] Example 3 (1) Stepwise esterification reaction: 146.2 g (1.0 mol) TMPD and 262.5 g (2.15 mol) benzoic acid were added to a 1000 mL reactor. Composite catalysts were added: 0.34 g tetraisobutyl titanate (approximately 0.001 mol) and 0.31 g dibutyltin dilaurate (approximately 0.0005 mol, with a molar ratio of organotitanium to tin of approximately 1:0.5), with an addition amount of approximately 0.16%. First stage: under normal pressure (without deliberate pressurization but in a sealed environment), the reaction was carried out at 150 ℃ for 1.5 hours; after venting, the reaction proceeded to the second stage: 20 mL xylene was added as a dehydrating agent, the system temperature was raised to 175 ℃, the system pressure was reduced to 10 kPa, and the reaction was carried out continuously for 4 hours.

[0037] (2) Neutralization wash: Cool to 70 °C, neutralize with 150 mL of 10% sodium carbonate aqueous solution, and then wash with 70 °C water until neutral.

[0038] (3) Light content removal and viscosity reduction by scraped-film molecular distillation: After adding an anti-yellowing agent (same as in Example 1), light content was removed for 1 hour at 130℃ and 1000 Pa. The moisture content was found to be 0.05%. 0.1 m... 2 A scraped-film molecular evaporator, with a controlled heating surface temperature of 200 ℃, a system vacuum of 10 Pa, and a feed rate of 2.0 L / H (equivalent to a flux of 20 L / (m²)). 2 •h), rotation speed 400 r / min. Built-in condenser temperature set to 85 ℃.

[0039] Results: Yield 96.1%, GC total ester purity 96.9%, diester content 94.1%, no visible mechanical impurities, moisture 0.04%, acid value 0.05 mg KOH / g, platinum-cobalt color 52.

[0040] Example 4 (1) Stepwise esterification reaction: 146.2 g (1.0 mol) TMPD and 258.9 g (2.12 mol) benzoic acid were added to a 1000 mL reactor. A composite catalyst was added: 0.17 g tetrabutyl titanate (approximately 0.0005 mol) and 0.20 g stannous isooctanoate (approximately 0.0005 mol, with an organotitanium to tin molar ratio of approximately 1:1). First stage: Under closed pressure of 0.11 MPa, the reaction was carried out at 145 ℃ for 2.5 hours; after venting, the reaction proceeded to the second stage: 25 mL of toluene was added as a dehydrating agent, the temperature was raised to 172 ℃, and the system pressure was reduced to 20 kPa for continuous reaction for 6 hours.

[0041] (2) Neutralization wash: Cool to 65 ℃, neutralize with 8% sodium carbonate aqueous solution, and then wash with 65 ℃ water until neutral.

[0042] (3) Light content removal and viscosity reduction by scraped-film molecular distillation: After adding an anti-yellowing agent (same as in Example 1), light content was removed to a moisture content of 0.07%. A 0.1 m³ pump was used for purification. 2 A scraped-film molecular evaporator, with the heating surface temperature controlled at 180 ℃, a system vacuum of 100 Pa, and a feed rate of 1.5 L / H (equivalent to a flux of 15 L / (m²)). 2 •h), rotation speed 350r / min. Built-in condenser temperature set to 80℃.

[0043] Results: Yield 94.8%, GC total ester purity 96.3%, diester content 92.8%, no visible mechanical impurities, moisture 0.06%, acid value 0.04 mg KOH / g, platinum-cobalt color 48.

[0044] Example 5 (1) Stepwise esterification reaction: 146.2 g (1.0 mol) TMPD and 254.0 g (2.08 mol) benzoic acid were added to a 1000 mL reactor. A composite catalyst was added: 0.17 g tetraisobutyl titanate (approximately 0.0005 mol) and 0.19 g dibutyltin oxide (approximately 0.00075 mol, with an organotitanium to tin molar ratio of approximately 1:1.5). First stage: The pressure was increased to 0.13 MPa, and the temperature was controlled at 135 ℃ for 2 hours. Second stage: 20 mL of cyclohexane was added as a dehydrating agent, the temperature was increased to 165 ℃, and the system pressure was reduced to 15 kPa for continuous reaction for 7 hours.

[0045] (2) Neutralization wash: Cool to 60 ℃, neutralize with 5% sodium bicarbonate aqueous solution, and wash with 60 ℃ water until neutral.

[0046] (3) Light content removal and viscosity reduction by scraped-film molecular distillation: After adding an anti-yellowing agent (same as in Example 1), light content was removed to a moisture content of 0.04%. 0.1 m³ of water was pumped in. 2 A scraped-film molecular evaporator, with a controlled heating surface temperature of 190 ℃, a system vacuum of 500 Pa, and a feed rate of 1.2 L / H (equivalent to a flux of 12 L / (m³)). 2 •h), rotation speed 300 r / min. Built-in condenser temperature set to 75 ℃.

[0047] Results: Yield 95.1%, GC total ester purity 96.6%, diester content 93.7%, no visible mechanical impurities, moisture 0.03%, acid value 0.03 mg KOH / g, platinum-cobalt color 44.

[0048] Comparative Example 1 The synthesis and purification process of this comparative example is basically the same as that of Example 1, except that in step (1), stannous isooctanoate was not added, and only 0.60 g of tetraisopropyl titanate was used as a single catalyst. The remaining feed amounts, equipment parameters and operating steps are consistent with those of Example 1.

[0049] Results: The reaction rate in the second stage was slow, and a single titanium catalyst was insufficient to overcome the steric hindrance of the C3 secondary hydroxyl group. After purification by molecular distillation, the final total ester yield was only 65.2%, GC analysis showed a high residual amount of monoester, a diester content of only 82.3%, and a platinum-cobalt color of 85.

[0050] Comparative Example 2 The synthesis and purification process of this comparative example is basically the same as that of Example 1, except that in step (1), tetraisopropyl titanate was not added, and only 0.60 g of stannous isooctanoate was used as a single catalyst. All other operating parameters are the same.

[0051] Results: The catalytic activity was insufficient at 170 °C, failing to effectively promote secondary esterification. The yield was 81.3%, the total ester purity by GC was 95.4%, the diester content was 85.6%, and the product's platinum-cobalt color reached 90.

[0052] Comparative Example 3 The synthesis and purification process of this comparative example is basically the same as that of Example 1, except that the composite catalyst is replaced with 1.5 g of strong protic acid, namely p-toluenesulfonic acid (p-TSA), and no anti-yellowing agent is added.

[0053] Results: The strong acid caused numerous side reactions, generating a large amount of olefinic impurities. The final distillate yield was only 61.5%, the GC total ester purity dropped to 84.1%, the diester content was as low as 60.5%, and the product exhibited a distinct yellowish-brown color with a platinum-cobalt color index >200.

[0054] Comparative Example 4 The synthesis and purification process of this comparative example is basically the same as that of Example 1, except that the first stage of the 140 °C reaction is omitted, and the material is directly heated to 190 °C in the second stage and reacted continuously under normal pressure.

[0055] Results showed that at a high temperature of 190 ℃, the ligand alcohol released by tetraisopropyl titanate was more likely to undergo transesterification with benzoic acid. After molecular distillation, the total ester yield decreased to 86.4%, and GC analysis revealed approximately 4.5% mixed ester impurities (such as isopropyl benzoate) in the system. The diester content was only 91.1%, and the platinum-cobalt color was 65.

[0056] Comparative Example 5 The synthesis and neutralization washing steps of this comparative example are exactly the same as those of Example 1. The core difference is that in step (3), instead of using a scraped membrane molecular evaporator, a conventional industrial "pot-type vacuum distillation column with packed tower" is used for end purification, and the bottom of the pot is heated to above 220 °C at 50 Pa to distill off the product.

[0057] Results showed that the prolonged high-temperature thermal process (residual time of several hours) caused some diesters to undergo transesterification degradation, reducing the diester content to 90.3% and causing a certain degree of yellowing in the product. The final product achieved a platinum-cobalt color intensity of 110.

[0058] Comparative Example 6 The process of this comparative example is basically the same as that of Example 1, except that the ratio of the composite catalyst is changed, and 0.40 g of tetraisopropyl titanate and 0.05 g of stannous isooctanoate are added (the molar ratio of organic titanium to tin is about 1:0.08).

[0059] Results showed that the proportion of tin was low, which affected the reaction kinetics to some extent. The total ester yield of the distillate was 87.2%, the diester content was 89.4%, and the platinum-cobalt color was 75.

[0060] Comparative Example 7 The process for this comparative example is basically the same as that for Example 1, except that organotin is replaced with organozinc. 0.15 g of tetraisopropyl titanate and 0.35 g of zinc isooctanoate are added.

[0061] Results showed that the product yield was 84.1%, diester content was 86.5%, and platinum-cobalt color was 105. This indicates that conventional zinc metal is unlikely to achieve the excellent synergistic effect of replacing tin.

[0062] Comparative Example 8 The synthesis and light-removal steps in this comparative example are exactly the same as in Example 1. The only key difference is that, in the operation of the scraped film molecular evaporator, the circulating water temperature of the built-in condenser is changed to conventional 25°C room temperature cooling water.

[0063] Results and phenomena: When the vaporized high-viscosity product comes into contact with the condensation surface at 25 ℃, a viscous liquid film with poor flowability is formed due to the low temperature, which cannot flow smoothly to the collection tank at the bottom. The liquid film gradually accumulates and comes into contact with the rotor, affecting the stable operation of the scraper rotor, causing fluctuations in the vacuum system, and ultimately making it difficult to continuously collect effective products.

[0064] Comparative Example 9 The synthesis and neutralization washing steps of this comparative example are exactly the same as those of Example 1. The key difference is that in the depressurization removal stage of step (3), the removal time is shortened so that the moisture content of the crude product mixture before entering the scraped membrane molecular distillation apparatus is retained at 0.5% (greater than 0.10%).

[0065] Results showed that the product yield was 90.1%, the diester content was 93.8%, and the platinum-cobalt color was 85.

[0066] Results and Measurements: When material containing 0.5% moisture enters a scraped-film molecular evaporator at 50 Pa and a heating surface temperature of 170 ℃, the free water undergoes significant flash evaporation and volume expansion (i.e., violent boiling). Some unvaporized heavy components and impurities are splashed onto the built-in condenser surface along with the airflow. The final collected distillate product appears turbid, and suspended mechanical impurities are visible to the naked eye. As a result, the platinum-cobalt color (Pt-Co) of the product increases to 85.

[0067] The core technical data of each embodiment and the comparative example are compared in the table below:

[0068] refer to Figure 2 and Figure 3 As shown, to visually demonstrate the difference in color, the prepared 2,2,4-trimethyl-1,3-pentanediol dibenzoate was placed in a 20ml colorless transparent glass bottle and photographed. Examples 1, 1, 3, and 3 were arranged together in sequence to form... Figure 2 Example 4, Comparative Example 4, Example 5, Comparative Example 5, and Comparative Example 9 are arranged in sequence to form... Figure 3 .Depend on Figure 2 and Figure 3 It can be clearly observed that the 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared by the method provided in this invention has low color intensity and light color.

[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A process for synthesizing 2,2,4-trimethyl-1,3-pentanediol dibenzoate, comprising the following steps: Step (1) Step-by-step esterification reaction: 2,2,4-trimethyl-1,3-pentanediol and benzoic acid are mixed, a composite catalyst is added, and a step-by-step esterification dehydration reaction is carried out under heating conditions to obtain a crude ester reaction solution. The composite catalyst is a mixture of organotitanium compounds and organotin compounds, and the molar ratio of organotitanium compounds to organotin compounds is 1:0.5 to 1:

3. The step-by-step esterification dehydration reaction includes the following two controlled stages: First stage reaction: The temperature of the reactants is controlled at 130-150 ℃, and the reaction is kept at a slightly pressurized closed state at atmospheric pressure to less than 0.15 MPa for 1-3 hours. After the heat preservation is completed, the pressure is released to remove some of the small molecule alcohol ligands dissociated from the composite catalyst from the system. Second stage reaction: An azeotropic dehydrating agent is added, the system is heated to 160-175 ℃, and the reaction is carried out continuously for 4-8 hours under the condition that the absolute pressure of the system is reduced to 10-40 kPa. Step (2) Neutralization and washing: After the reaction is completed, the crude ester reaction solution is cooled down, and an alkaline aqueous solution is added for neutralization and washing. After separating the aqueous phase, the organic phase is washed with water until neutral. Step (3) Light component removal and viscosity reduction / flow-promoting molecular distillation purification: Add an anti-yellowing agent to the organic phase after washing in step (2), and remove light components under reduced pressure at 100-130 ℃ and 1000-5000 Pa absolute pressure to remove water-carrying agent and water; then continuously pump the crude product into a scraped membrane molecular distillation apparatus for high vacuum purification, control the temperature of the heating surface of the evaporator at 150-200 ℃, and the absolute vacuum of the system at 10-200 Pa; control the temperature of the built-in condenser surface of the scraped membrane molecular distillation apparatus at 65-85 ℃, vaporize the target product 2,2,4-trimethyl-1,3-pentanediol dibenzoate and liquefy it on the built-in condenser surface, collect it as distillate, and at the same time discharge heavy component impurities from the bottom of the equipment.

2. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: The amount of the composite catalyst added is 0.05% to 0.3% of the total mass of the reactants; the organotitanium compound is selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, or tetraisobutyl titanate; the organotin compound is selected from one or more of dibutyltin oxide, dibutyltin dilaurate, or stannous isooctanoate.

3. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: The initial molar ratio of 2,2,4-trimethyl-1,3-pentanediol to benzoic acid is 1:2.02 to 1:2.15; the azeotropic dehydrating agent is selected from one or more of toluene, xylene, or n-butyl ether.

4. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: The anti-yellowing agent is selected from pentaerythritol di(2,4-di-tert-butylphenyl) phosphite or diisodecyl phosphite.

5. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: In step (2), after cooling to 60-70°C, a 5%-10% sodium carbonate or sodium bicarbonate aqueous solution is added for neutralization.

6. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: The operating parameters of the scraped-film molecular distillation apparatus in step (3) are as follows: the feed throughput of the material is controlled at 5–20 L / (m²). 2 (h), the speed of the built-in rotor of the equipment is controlled at 200-400 r / min, so that the average residence time of the material on the heated surface does not exceed 60 seconds.

7. The synthesis process of 2,2,4-trimethyl-1,3-pentanediol dibenzoate according to claim 1, characterized in that: In the dehydration step (3), the dehydration endpoint is controlled so that the water content in the crude organic phase is reduced to below 0.10%.

8. A 2,2,4-trimethyl-1,3-pentanediol dibenzoate prepared according to any one of claims 1 to 7, characterized in that: The 2,2,4-trimethyl-1,3-pentanediol dibenzoate is a pale yellow to colorless transparent liquid with a water content ≤ 0.10%, a total ester purity ≥ 96.0% by gas chromatography, wherein the diester content is between 92.5% and 95.0%, the acid value is ≤ 0.05 mg KOH / g, and the platinum-cobalt color (Pt-Co) is between 40 and 55.

Images