A method for preparing pentaerythritol stearate

Abstract

A method for preparing pentaerythritol stearate belongs to the field of ester synthesis technology in organic chemistry. First, a zinc salt or its oxide reacts with a carboxyl-terminated hyperbranched polymer to obtain hyperbranched zinc carboxylate. Then, using pentaerythritol and stearic acid as raw materials, an esterification reaction is carried out under a nitrogen atmosphere with the action of a hyperbranched zinc carboxylate solid catalyst to obtain the pentaerythritol stearate solid product. This invention rationally selects a novel solid catalyst, which generates almost no byproducts, requires no recovery, provides mild reaction conditions, requires no post-treatment, does not corrode equipment, and has a simple production process.

Description

Technical Field

[0001] This invention relates to a method for preparing pentaerythritol stearate, belonging to the field of ester synthesis technology in organic chemistry. Background Technology

[0002] Pentaerythritol stearate is a white, hard, high-melting-point wax or white powder. It is soluble in ethanol, benzene, and chloroform, but insoluble in water. It is widely used as an auxiliary heat stabilizer, plasticizer, and lubricant in the rubber and plastics industries. Hundreds of thousands of tons of such lubricants are needed annually for plastic processing products, indicating a broad market prospect.

[0003] The traditional preparation method for pentaerythritol stearate involves an esterification reaction of pentaerythritol and stearic acid under acidic or alkaline catalysts at high temperatures. Toluenesulfonic acid catalysts offer high activity, few side reactions, and a light-colored product, achieving esterification rates exceeding 96%. However, they require post-treatment with neutralization water washing, generating wastewater. Concentrated sulfuric acid catalysts are extremely low-cost and fast; however, they easily lead to carbonization, oxidation, product yellowing, and equipment corrosion, limiting their use to low-end processes. Phosphoric acid and phosphorous acid catalysts are mildly acidic, with few side reactions and good color, but their catalytic activity is relatively weak, requiring higher temperatures and longer processing times. In Chinese invention patent applications CN 104557535 A and CN 104610052 A, stannous chloride is used as a catalyst, and the yield of pentaerythritol stearate is 76%, which is relatively low. In Chinese invention patent CN 105753698 B, a Zn-Al catalyst is used, achieving a pentaerythritol stearate yield of 98.4%, but the catalyst preparation process is cumbersome and not easily industrialized. Therefore, developing a catalyst with high yield, easy preparation, solvent-free catalytic reaction, and no need for recovery is key to realizing the industrialization of pentaerythritol stearate. Summary of the Invention

[0004] To address the problems of large amounts of organic solvents, complex catalyst preparation methods, difficult catalyst separation, and low yield in the current preparation process of pentaerythritol stearate, this invention provides a solvent-free method for preparing pentaerythritol stearate. Compared with existing technologies, the solvent-free pentaerythritol stearate prepared by this invention does not use organic solvents such as toluene and xylene throughout the entire process, has no VOC emissions, requires no solvent recovery, produces no wastewater, leaves no solvent residue, and is not highly corrosive. It is equipment-friendly, promotes clean production, and is more environmentally friendly. It requires no neutralization or washing, introduces no impurities from solvents, requires no post-treatment, and does not require solvent removal. The product has good whiteness and light color, making it suitable for high-end lubricants and plastic processing aids.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: (1) Synthesis of hyperbranched zinc carboxylate: Weigh out zinc metal salt or its oxide, terminal carboxyl hyperbranched polymer, add water as solvent, react for a period of time, cool, filter and dry after the reaction to obtain hyperbranched zinc carboxylate; (2) Using pentaerythritol and stearic acid as raw materials, hyperbranched zinc carboxylate as a solid catalyst, an esterification reaction is carried out under a nitrogen atmosphere, and pentaerythritol stearate is obtained after the reaction is complete; the molar ratio of pentaerythritol to stearic acid is 1: (3.4~4.0).

[0006] Furthermore, the zinc salt is one or both of zinc carbonate and zinc acetate, and the oxide is zinc oxide.

[0007] Furthermore, the molar ratio of the zinc salt or its oxide to the carboxyl groups in the carboxyl-terminated hyperbranched polymer is 1:1-3.

[0008] Furthermore, the terminal carboxyl hyperbranched polymer has a molecular weight of 950~13200 g / mol and an acid value of 110~360 mg KOH / g.

[0009] Furthermore, the terminal carboxyl hyperbranched polymer is derived from one or more of the HyPer C101, HyPer C102, HyPer C103, HyPer C104, HyPer C201, HyPer C202, HyPer C203, HyPer C204, HyPer C301, HyPer C302, HyPer C303, HyPer C304, HyPer C401, HyPer C402, HyPer C403, and HyPer C404 series products from Wuhan Hyperbranched Resin Technology Co., Ltd., and their properties are shown in Table 1.

[0010] Table 1 Properties of terminal carboxyl hyperbranched polymers

[0011] Furthermore, the catalyst is added in an amount of 0.5% to 1.0% of the total weight of pentaerythritol and stearic acid.

[0012] Furthermore, the esterification reaction is carried out at a temperature of 160-230°C; and / or The esterification reaction takes 5-9 hours.

[0013] Furthermore, the reaction temperature in step (1) is 50-70℃ and the reaction time is 0.5-1h.

[0014] Compared with the prior art, the present invention has the following outstanding advantages and beneficial effects: (1) Green and environmentally friendly, with no solvent pollution: No organic solvents such as toluene, xylene, and petroleum ether are used throughout the process, there are no VOC emissions, no solvent recovery or distillation processes, thus avoiding solvent residue and meeting environmental protection production requirements.

[0015] (2) Simple process and high production efficiency: The reaction system consists of only pentaerythritol, stearic acid and hyperbranched zinc carboxylate catalyst. The equipment is simple and the operation steps are few. Hyperbranched zinc carboxylate can be directly dispersed in molten stearic acid, which is homogeneous catalysis, well dispersed and uniform reaction, without the need for additional solubilizer. High temperature direct esterification results in a faster reaction rate and higher yield.

[0016] (3) Lower cost, less energy consumption and less waste: Saves the cost of solvent procurement, recycling and post-treatment; no energy consumption of solvent distillation, wastewater, waste gas and waste residue are greatly reduced, the cost of treating waste is low, and it is suitable for continuous industrial production.

[0017] (4) High product purity and light color: No solvent introduces impurities, the product post-processing is simple, no catalyst removal is required, the hyperbranched zinc carboxylate catalyst remains in the product and not only has no negative impact, but can also synergistically lubricate, improve dispersion and assist in thermal stability. No solvent removal is required, the acid value is low, the hydroxyl value is controllable and the purity is high. Compared with concentrated sulfuric acid and p-toluenesulfonic acid, hyperbranched zinc carboxylate has weak acidity, does not corrode equipment, has low equipment wear, and hardly causes the material to turn black or yellow at high temperature. The product has good whiteness and light color, and is suitable for high-end lubricants and plastic processing aids. Attached Figure Description

[0018] Figure 1 These are photographs of pentaerythritol stearate block and powder samples prepared in Example 1 of this invention.

[0019] Figure 2 This is the infrared spectrum of pentaerythritol stearate prepared in Example 1 of this invention.

[0020] Figure 3 This is the DSC spectrum of pentaerythritol stearate prepared in Example 1 of this invention. Detailed Implementation

[0021] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The terminal carboxyl hyperbranching was purchased from Wuhan Hyperbranching Resin Technology Co., Ltd., and the relevant properties are shown in Table 1. The stearic acid used was mixed stearic acid (containing 40 wt% C). 18 H 36 O2, 60wt% C 16 H 32O2 (originating from Zhangjiagang), with an average molecular weight of 267.64, uses commercially available raw materials.

[0022] Step (1) Synthesis of hyperbranched zinc carboxylate catalyst: Weigh 1.0g of zinc oxide and 6.4g of end-carboxyl hyperbranched polymer HyPer C103, add an appropriate amount of water as solvent, react at 50℃ for 1h, after the reaction is completed, cool, filter, wash, and dry under vacuum at 100℃ to obtain the catalyst hyperbranched zinc carboxylate. Step (2) Synthesis of pentaerythritol stearate: Weigh 532.15g stearic acid, 67.85g pentaerythritol, and 6.00g hyperbranched zinc carboxylate and add them to a three-necked flask. Purge with nitrogen for 3 minutes to remove air from the system. Then, under nitrogen protection, heat and stir the reaction. When the temperature reaches 170℃, pentaerythritol and hyperbranched zinc carboxylate are completely dispersed in the molten stearic acid. Continue to heat the system, increasing the temperature by 10℃ every 1 hour. After the reaction temperature reaches 210℃, stop heating and maintain this temperature. During the reaction, test the acid value of the system. When the acid value is less than 5mgKOH / g (the measured value in this example is 4.65mgKOH / g), stop the reaction and pour out the product. The reaction time is 7.5 hours. After cooling, pentaerythritol stearate solid is obtained (e.g., Figure 1 Its infrared spectrum is as follows Figure 2 As shown, at 1735 cm -1 The presence of a characteristic absorption peak near the carbonyl group indicates the successful synthesis of pentaerythritol stearate, with a yield of 99.8% and a melting point of 66.0℃ (DSC spectrum as shown). Figure 3 ).

[0023] Example 2: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: Step (1) Synthesis of hyperbranched zinc carboxylate catalyst: Weigh 1.5g of zinc carbonate and 5.2g of end-carboxyl hyperbranched polymer HyPer C203, add an appropriate amount of water as solvent, react at 60℃ for 0.8h, after the reaction is completed, cool, filter, and vacuum dry at 105℃ to obtain hyperbranched zinc carboxylate; Step (2) Synthesis of pentaerythritol stearate: Weigh 52.83g stearic acid, 7.17g pentaerythritol and 0.6g hyperbranched zinc carboxylate and add them to a three-necked flask. Purge with nitrogen for 3 minutes to remove air from the system. Then, under nitrogen protection, heat and stir the reaction. When the temperature reaches 170℃, pentaerythritol and hyperbranched zinc carboxylate are completely dispersed in the molten stearic acid. Continue to heat the system, increasing the temperature by 10℃ every 1 hour. After the reaction temperature reaches 220℃, stop heating and maintain this temperature. During the reaction, test the acid value of the system. When the acid value of the system is less than 5mgKOH / g (the measured value in this example is 4.67mgKOH / g), stop the reaction and pour out the product. The reaction time is 7.6 hours. After cooling, pentaerythritol stearate solid is obtained with a yield of 99.5% and a melting point of 67.0℃.

[0024] Example 3: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: Step (1) Synthesis of hyperbranched zinc carboxylate catalyst: Weigh 2.2g of zinc acetate and 4.9g of carboxyl-terminated hyperbranched polymer HyPer C304, add an appropriate amount of water as solvent, react at 70℃ for 0.5h, after the reaction is completed, cool, filter, and vacuum dry at 110℃ to obtain hyperbranched zinc carboxylate; Step (2) Synthesis of pentaerythritol stearate: Weigh 105.31g stearic acid, 14.69g pentaerythritol and 0.6g hyperbranched zinc carboxylate and add them to a three-necked flask. Purge with nitrogen for 3 minutes to remove air from the system. Then, under nitrogen protection, heat and stir the reaction. When the temperature reaches 170℃, pentaerythritol and hyperbranched zinc carboxylate are completely dispersed in the molten stearic acid. Continue to heat the system, increasing the temperature by 10℃ every 1 hour. After the reaction temperature reaches 220℃, stop heating and maintain this temperature. During the reaction, test the acid value of the system. When the acid value of the system is less than 5mgKOH / g (the measured value in this example is 3.90mgKOH / g), stop the reaction and pour out the product. The reaction time is 9 hours. After cooling, pentaerythritol stearate solid is obtained with a yield of 99.7% and a melting point of 68.0℃.

[0025] Example 4: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: Step (1) Synthesis of hyperbranched zinc carboxylate catalyst: Weigh 0.65g of zinc oxide and 6.8g of end-carboxyl hyperbranched polymer HyPer C402, add an appropriate amount of water as solvent, react at 50℃ for 1h, after the reaction is completed, cool, filter, and vacuum dry at 115℃ to obtain hyperbranched zinc carboxylate; Step (2) Synthesis of pentaerythritol stearate: Weigh 100.52g stearic acid, 15.04g pentaerythritol and 1.2g hyperbranched zinc carboxylate and add them to a three-necked flask. Purge with nitrogen for 3 minutes to remove air from the system. Then, under nitrogen protection, heat and stir the reaction. When the temperature reaches 170℃, pentaerythritol and hyperbranched zinc carboxylate are completely dispersed in the molten stearic acid. Continue to heat the system, increasing the temperature by 10℃ every 1 hour. After the reaction temperature reaches 230℃, stop heating and maintain this temperature. During the reaction, test the acid value of the system. When the acid value of the system is less than 5mgKOH / g (the actual measured value in this example is 3.37mgKOH / g), stop the reaction and pour out the product. The reaction time is 10 hours. After cooling, pentaerythritol stearate solid is obtained with a yield of 99.3% and a melting point of 69.0℃.

[0026] Comparative Example 1: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: 532.15 g of stearic acid, 67.85 g of pentaerythritol, and 6 g of anhydrous stannous chloride were weighed and added to a three-necked flask. Nitrogen gas was purged for 3 minutes to remove air from the system. Then, under nitrogen protection, the mixture was heated and stirred. When the temperature reached 170 °C, the pentaerythritol and anhydrous stannous chloride were completely dispersed in the molten stearic acid. The temperature was increased by 10 °C every 1 hour. After the reaction temperature reached 220 °C, the temperature was maintained at that temperature. The acid value of the system was tested during the reaction. When the acid value was less than 5 mg KOH / g (the measured value in this example was 4.95 mg KOH / g), the reaction was stopped and the product was poured out. The reaction time was 15 hours. After cooling, pentaerythritol stearate solid was obtained with a yield of 78.2%. Two melting temperatures were observed in the sample, namely 65.0 °C and 67.0 °C.

[0027] Comparative Example 2: A method for preparing pentaerythritol stearate, the specific steps of which are as follows: Weigh 532.15g of stearic acid, 67.85g of pentaerythritol, 200mL of xylene, and 6g of p-toluenesulfonic acid into a three-necked flask. Purge the system with nitrogen for 10 minutes to remove air. Then, under nitrogen protection, heat and stir the reaction mixture. Once the stearic acid and p-toluenesulfonic acid have completely melted at 130℃, continue heating by increasing the temperature by 10℃ every hour. After reaching 160℃, stop heating and maintain this temperature. Keep the water separator continuously discharging water and strictly record the amount of water discharged until no more water is generated in the separator. Test the acid value of the system during the reaction. The acid value of the system should be less than 5mgKOH. The reaction was stopped when the concentration of KOH / g (the measured value in this example was 4.83 mg KOH / g) was reached. The reaction time was 7 h. The system was cooled to 90 °C, and a saturated NaHCO3 aqueous solution was slowly added dropwise. The mixture was stirred for 15-20 minutes, allowed to stand, and then the organic phase was washed with deionized water at 80 °C. The crude product of pentaerythritol stearate was obtained by rotary evaporation. The crude product was then dissolved by heating and reflux with 95% ethanol. The insoluble impurities were removed by hot filtration. The product was cooled to crystallize, filtered, and dried under vacuum at 60 °C to obtain a pale yellow pentaerythritol stearate solid with a yield of 88.3%. Two melting temperatures were observed in the sample, namely 50.0 °C and 74.0 °C.

[0028] Table 2. Acid value and saponification value test results of pentaerythritol stearate in each example and comparative example.

[0029] Although the present invention has been described in detail with general description and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing pentaerythritol stearate, characterized in that, The preparation method includes the following steps: Step (1) Synthesis of hyperbranched zinc carboxylate catalyst: Weigh out zinc metal salt or its oxide, terminal carboxyl hyperbranched polymer, add water as solvent, after the reaction is complete, cool, filter and dry to obtain hyperbranched zinc carboxylate; Step (2) Synthesis of pentaerythritol stearate: Using pentaerythritol and stearic acid as raw materials, and the hyperbranched zinc carboxylate obtained in step (1) as a solid catalyst, esterification reaction is carried out under a nitrogen atmosphere to obtain pentaerythritol stearate.

2. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that: The zinc salt is one or both of zinc carbonate and zinc acetate, and the oxide is zinc oxide.

3. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that: The terminal carboxyl hyperbranched polymer is one or more of HyPer C101, HyPer C102, HyPer C103, HyPer C104, HyPer C201, HyPer C202, HyPer C203, HyPer C204, HyPer C301, HyPer C302, HyPer C303, HyPer C304, HyPer C401, HyPer C402, HyPer C403, and HyPer C404 from Wuhan Hyperbranched Resin Technology Co., Ltd.

4. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that, The molar ratio of the zinc salt or its oxide to the carboxyl groups in the carboxyl-terminated hyperbranched polymer is 1:1-3.

5. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that, The molar ratio of pentaerythritol to stearic acid is 1:3.4~4.

0.

6. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that, In step (2), the amount of solid catalyst added is 0.5 to 1.0% of the total weight of pentaerythritol and stearic acid.

7. The method for preparing pentaerythritol stearate as described in claim 1, characterized in that, The reaction temperature in step (1) is 50-70℃ and the reaction time is 0.5-1h. The reaction temperature of the esterification reaction in step (2) is 160-230℃ and the reaction time is 5-9 hours.

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