Efficient purification method of bis (2, 2, 6, 6-tetramethyl-4-piperidyl) sebacate

Abstract

The invention relates to the technical field of chemical engineering and polymer auxiliaries, and particularly discloses an efficient purification method of bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate, when tetramethylpiperidinol and dimethyl sebacate are used for synthesizing bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate, the residual tetramethylpiperidinol in the reaction is converted into the bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate, and the bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate is obtained through the high-efficiency purification method of the bis (2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate. In the conventional water washing link, water washing removal is difficult, a large amount of waste water is generated, and amine-containing compounds and catalyst impurities easily cause oxidation yellowing and discoloration of the product; the washing purification step is optimized and improved, and the purposes of improving the washing efficiency, reducing the chromaticity of the product and not influencing the anti-aging application effect are achieved in the modes of removing chromophoric groups through acid washing, carrying out oxidation pretreatment and protecting hindered amine functional groups through alkali washing; in the whole process, water washing can be reduced from conventional 5-7 times to 2 times, so that the water washing efficiency is improved, and the excellent chromaticity index of the product is ensured; the method is high in practical operability, and industrial production can be stably operated.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical engineering and polymer additives, and specifically to a purification process for the production of hindered amine light stabilizers. Background Art

[0002] Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, also known as light stabilizer 770, is a representative hindered amine light stabilizer, which is widely used in various polymer materials and different application scenarios, has a good anti-photoaging effect, and when used in synergy with ultraviolet absorbers and antioxidants, can effectively extend the service life of polymer materials such as plastics and rubbers.

[0003] Currently, the common industrial preparation method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate is to synthesize it from tetramethylpiperidinol and dimethyl sebacate in a solvent atmosphere under the action of a catalyst through transesterification reaction, and by refluxing to separate methanol, and separating methanol by layering methanol and the solvent in a low-temperature separator, so as to make the reaction proceed in the forward direction. And, in subsequent processing, it is necessary to wash and remove the unreacted tetramethylpiperidinol by water washing to ensure that there is less tetramethylpiperidinol in the final product and to ensure higher purity of the product. Related reports [Li Kunquan et al. "Research on the Synthesis and Application of Hindered Amine Light Stabilizer 770." Synthetic Materials Aging and Application 48.5 (2019): 6.], [CN 114230511 A Preparation Method of Bis(2,2,6,6-Tetramethyl-4-Piperidyl) Sebacate].

[0004] The problems of the existing synthesis and water-washing purification are that when transesterifying to synthesize bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, the residual tetramethylpiperidinol in the reaction has a comparable partition coefficient in the organic phase solvent oil and hot water during water washing, and the single water-washing effect is not good. Generally, 5 - 7 times of water washing are required in industrial production, and on average, 1 ton of water-washing wastewater is generated per ton of product, which directly affects the production efficiency and brings great pressure to environmental protection treatment.

[0005] In addition, there is a literature report on the process of decolorization and purification using organic acids and reducing agents [CN 1161463685 A Synthesis Method of Hindered Amine Light Stabilizer 292]. The major problems of this process are that although it improves and enhances the product indexes, it has a serious negative impact on its application. The addition of weak acids, 1) leads to the weakening of its aging performance, and the retention rate of the tensile strength at break drops significantly compared with the product without acid washing; 2) although the addition of reducing agents achieves the effect of decolorization on the product indexes during the production process, it is still oxidized and discolored during the subsequent application process, and the discoloration problem cannot be fundamentally solved.

[0006] Therefore, there is an urgent need in the industry for a preparation method that can improve the water washing efficiency, reduce the color number of the product, and does not affect the later application performance, so as to achieve the purposes of reducing energy consumption, streamlining the production process, and reducing the three wastes. Summary of the Invention

[0007] To solve the problems raised in the above background art, the present invention provides an efficient purification method for bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate.

[0008] When synthesizing bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate by transesterification, in addition to the target product bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate and a small amount of tetramethyl piperidinol in the reaction solution, there are also a small amount of monoesterification products, as well as unilateral isopropyl ester or butyl ester exchange intermediate products catalyzed by the catalyst. In addition, there are also a small amount of amine-containing compounds in the reaction solution. There are two sources of amine compounds. One is that the raw material tetramethyl piperidinol contains trace amounts of tetramethyl piperidine amine and small molecule amines, and the other is the amine chloride introduced by the catalyst. The presence of these amine-containing substances will cause color change due to heating oxidation and rearrangement into a conjugated structure, increasing the chromaticity of the final product and turning it yellow. In addition, due to the quality fluctuation of the catalyst, the residual metal ions will deepen the color of the reaction and the product, making it difficult to remove. The above are all the general reasons for the discoloration and yellowing of the product.

[0009] In the application link, the functional group of the light stabilizer is a hindered amine group. When the amine group is acidified to form an ammonium salt, it loses its light stabilizer function (Chen Miaoqin, Sun Jianzhong, Jiang Yongbo, etc. Synthesis and Characterization of 1-Cyclohexyloxy-4-oxo-2,2,6,6-Tetramethylpiperidone [J]. Journal of Chemical Engineering of Chinese Universities, 2010, 24(3):5. DOI: CNKI:SUN:GXHX.0.2010-03-022.). Therefore, the pickling reported in related patents will make some of the 770 hindered amine groups lose their activity and affect their later anti-aging function.

[0010] Through a large number of studies, the present invention finds that by pickling to remove chromogenic groups, oxidative pretreatment, and alkali washing to protect the hindered amine functional groups, the purpose of improving the water washing efficiency, reducing the chromaticity of the product, and not affecting the anti-aging application effect can be achieved.

[0011] Specifically, in the water washing step: 1) By introducing an organic weak acid, the residual tetramethylpiperidinol is salted with a small amount of amino compounds, increasing its solubility in the aqueous phase and thus being efficiently washed away, effectively improving the water washing efficiency and reducing the residues of amino compounds and their oxides; 2) Then, the residual impurities in the catalyst are pre-oxidized by an oxidant; 3) Then, the pH is adjusted by adding alkali to neutralize the excessive acid, and the mixture is subjected to cyclic adsorption and filtration; finally, crystallization and drying are carried out to obtain a product with high purity and low chromaticity, generally improving the water washing efficiency and ensuring the anti-aging application effect of the product.

[0012] To achieve the above object, the present invention provides the following technical solutions: A method for efficiently purifying bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate of the present invention includes the following steps: Esterification reaction: Using tetramethylpiperidinol and dimethyl sebacate as raw materials, under a solvent atmosphere and with the action of a catalyst, a reaction solution of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate is prepared, and the reaction solution is subjected to efficient purification; the molar ratio of dimethyl sebacate to tetramethylpiperidinol is 1:1.9 - 1:1.99.

[0013] The specific steps of the efficient purification method include the following: (1) Acid washing: After the reaction is completed, hot water and an organic acid are added to the reaction solution, the temperature is controlled at 80 - 95 °C and stirred for 1 - 3 hours, and then left to stand for 0.5 - 3 hours. After standing, the lower aqueous layer is separated. (2) Pre-oxidation: An oxidant is added to the reaction solution after the acid washing in the previous step for pre-oxidation, the temperature is controlled at 50 - 55 °C and stirred for 1 - 2 hours, and then left to stand for 0.5 - 3 hours. After standing, the lower aqueous layer is separated. (3) Alkali washing: Hot water and a quantitative alkali are added to the reaction solution after the pre-oxidation in the previous step, the temperature is controlled at 80 - 95 °C and stirred for 1 - 3 hours, and then left to stand for 0.5 - 3 hours. After standing, the lower aqueous layer is separated. (4) Filtration, dehydration, crystallization, and drying: The upper layer liquid is circulated through an activated carbon filter, after reflux and water separation, crystallization and drying are carried out to obtain the finished product.

[0014] Further, in step (1), the mass ratio of the organic acid to tetramethylpiperidinol is 0.002 - 0.02:1; preferably, the mass ratio of the organic acid to tetramethylpiperidinol is 0.003 - 0.007:1.

[0015] Further, the organic acid is one or more of formic acid, acetic acid, citric acid, and benzoic acid.

[0016] Further, in step (2), the mass ratio of the oxidant to tetramethylpiperidinol is 0.003 - 0.01:1; preferably, the mass ratio of the oxidant to tetramethylpiperidinol is 0.003 - 0.005:1.

[0017] Further, the oxidant is one or more of hydrogen peroxide with a concentration of 20 - 70%.

[0018] Further, in step (3), the mass ratio of the base to tetramethylpiperidinol is 0.002 - 0.02:1, preferably, the mass ratio of the base to tetramethylpiperidinol is 0.003 - 0.007:1.

[0019] Further, the base is one or more of solids or liquids of sodium hydroxide, potassium hydroxide, triethanolamine, sodium carbonate, and sodium bicarbonate.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention optimizes the water washing of the transesterification reaction solution of bis(2,2,6,6 - tetramethyl - 4 - piperidyl) sebacate by using the method of first acid washing, then pre - oxidation, and then alkali washing, and then obtains the final product through filtration, dehydration, crystallization, and drying. The whole process can reduce the conventional water washing times from 5 - 7 times to 2 times, improve the water washing efficiency, the product yield reaches more than 99%, the appearance chromaticity is low, and the anti - aging application performance is ensured to be stable. This method has strong practical operability and can operate stably in industrial production. Description of the Drawings

[0021] Figure 1 It is the infrared spectrogram of groups A, B, and D in Example 3. Detailed Embodiments

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Example 1

[0023] In a 500 ml four-necked flask equipped with a reflux water separator, add 154 g of tetramethylpiperidinol, 115 g of dimethyl sebacate, 3 g of tetrabutyl titanate, and 300 g of petroleum ether. Start stirring and heat up the reaction to control the internal temperature of the flask at 105 - 135 °C for 24 hours. After the reaction is completed, add 20 g of hot water to the reaction solution, and add 1 g of acetic acid. Stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower layer of water; continue to add 2.5 g of 35% hydrogen peroxide to the upper layer of the reaction solution, stir at 55 °C for 1 hour, let it stand for half an hour and then separate the lower layer of water; continue to add 20 g of hot water and 1 g of sodium hydroxide to the upper layer of the solution, stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower layer of water; finally, circulate and filter the upper layer of the reaction solution obtained finally through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 99.3%, and the detected chromaticity is 1. Example 2

[0024] In a 500 ml four-necked flask equipped with a reflux water separator, add 155.4 g of tetramethylpiperidinol, 115 g of dimethyl sebacate, 3 g of isopropyl titanate, and 300 g of petroleum ether. Start stirring and heat up the reaction to control the internal temperature of the flask at 105 - 135 °C for 24 hours. After the reaction is completed, add 20 g of hot water to the reaction solution, and add 0.8 g of acetic acid. Stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower layer of water; continue to add 1.8 g of 35% hydrogen peroxide to the upper layer of the reaction solution, stir at 55 °C for 1 hour, let it stand for half an hour and then separate the lower layer of water; continue to add 20 g of hot water and 1.5 g of triethanolamine to the upper layer of the solution, stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower layer of water; finally, circulate and filter the upper layer of the reaction solution obtained finally through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 99.4%, and the detected chromaticity is 2. Example 3

[0025] In a 2000 ml four-necked flask equipped with a reflux water separator, add 621.6 g of tetramethylpiperidinol, 460 g of dimethyl sebacate, 12 g of isopropyl titanate, and 1200 g of petroleum ether. Start stirring and heat up the reaction to control the internal temperature of the flask at 105 - 135 °C for 24 hours. After the reaction is completed, divide the reaction solution into 4 equal parts, namely 4 groups of A, B, C, and D. Treat them separately: The reaction solution of group A is treated by water washing. Add 20 g of hot water to the reaction solution, stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower layer of water; repeat 2 times in total. Finally, circulate and filter the upper layer of the reaction solution obtained finally through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 98.9%, and the detected chromaticity is 25.

[0026] Washing treatment of the reaction solution in Group B. Add 20 g of hot water to the reaction solution, and add 0.8 g of acetic acid. Stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower-layer water; continue to add 20 g of hot water to the upper-layer reaction solution, stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower-layer water. Finally, circulate and filter the finally obtained upper-layer reaction solution through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 99.3%, and the detected chromaticity is 4.

[0027] Washing treatment of the reaction solution in Group C. Add 20 g of hot water to the reaction solution, and add 0.8 g of acetic acid. Stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower-layer water; continue to add 1.8 g of 35% hydrogen peroxide to the upper-layer reaction solution, stir at 55 °C for 1 hour, let it stand for half an hour, and then separate the lower-layer water; finally, circulate and filter the finally obtained upper-layer reaction solution through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 99.2%, and the detected chromaticity is 2.

[0028] Washing treatment of the reaction solution in Group D. Add 20 g of hot water to the reaction solution, and add 0.8 g of acetic acid. Stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower-layer water; continue to add 1.8 g of 35% hydrogen peroxide to the upper-layer reaction solution, stir at 55 °C for 1 hour, let it stand for half an hour, and then separate the lower-layer water; continue to add 20 g of hot water and 1 g of sodium hydroxide to the upper layer, stir at 80 °C for 1 hour, let it stand for 1 hour, and separate the lower-layer water; finally, circulate and filter the finally obtained upper-layer reaction solution through an activated carbon filter, reflux and dehydrate, crystallize, and dry to obtain the final product. The product yield is 99%, the GC purity is 99.4%, and the detected chromaticity is 2.

[0029] The results of the 4 groups of control experiments and the aging results are as follows Figure 1 and Table 1: It can be seen from Figure 1 that the peak at 3410 cm -1 is the O-H stretching vibration peak, and the peak at 1380 cm -1 is the -CH3 bending vibration peak. Group A is conventional water washing, and the O-H peak weakens not significantly, indicating that there is more TMP residue; Group B uses acid washing, and the O-H peak weakens, indicating that TMP is effectively removed, but there is residue at -CH3 at 1380 cm-1, which may be due to the substitution of acetic acid; Group D is washed with acid and then neutralized with alkali, and the O-H peak weakens significantly, indicating that TMP is effectively removed, and -CH3 at -1 is significantly weakened, indicating that acetic acid is effectively neutralized and removed.

[0030] Table 1

[0031] As can be seen from the above table, the samples in Group B that were only treated with acid were pulverized after aging for 500 hours, indicating that the anti-aging performance of the prepared products is very poor; moreover, neither Group A nor Group B carried out pre-oxidation for impurity filtration, and both had a slightly yellow appearance after aging for 500 hours; Group C underwent pre-oxidation and remained white in color after aging for 500 hours, but due to the lack of alkali washing treatment, it was also pulverized at 500 hours, and its aging property was greatly affected; Group D underwent pre-oxidation and alkali washing, its aging performance was not greatly affected, and it could maintain a stable appearance during long-term application.

[0032] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such process, method, article or device.

[0033] It should be noted that the above content only illustrates the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. For those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements all fall within the protection scope of the claims of the present invention.

Claims

1. An efficient purification method for bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, comprising the following steps: Using tetramethylpiperidinol and dimethyl sebacate as raw materials, reacting them under a solvent atmosphere and in the presence of a catalyst to obtain a reaction solution of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, which is characterized by further comprising the following steps: After the reaction is completed, add hot water and organic acid to the reaction solution, control the temperature at 80 - 95 °C and stir for 1 - 3 hours, and then stand for 0.5 - 3 hours. After standing, separate the lower aqueous layer. Add an oxidant to the reaction solution after the pickling in the previous step for pre-oxidation, control the temperature at 50 - 55 °C and stir for 1 - 2 hours, and then stand for 0.5 - 3 hours. After standing, separate the lower aqueous layer. Add hot water and a base to the reaction solution after the pre-oxidation in the previous step, control the temperature at 80 - 95 °C and stir for 1 - 3 hours, and then stand for 0.5 - 3 hours. After standing, separate the lower aqueous layer. Finally, circulate and filter the upper layer liquid obtained in step (3) through an activated carbon filter. After reflux and water separation, crystallize and dry to obtain the finished product.

2. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 1, characterized in that, In step (1), the mass ratio of the organic acid to tetramethylpiperidinol is 0.002 - 0.02:

1.

3. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 2, characterized in that, The organic acid is one or more of formic acid, acetic acid, citric acid, and benzoic acid.

4. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 1, characterized in that, In step (2), the mass ratio of the oxidant to tetramethylpiperidinol is 0.003 - 0.01:

1.

5. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 4, characterized in that, The oxidant is one or more of hydrogen peroxide with a concentration of 20 - 70%.

6. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 1, characterized in that, In step (3), the mass ratio of the base to tetramethylpiperidinol is 0.002 - 0.02:

1.

7. The high-efficiency purification method of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate according to claim 6, characterized in that, The base is one or more of sodium hydroxide, potassium hydroxide, triethanolamine, sodium carbonate, and sodium bicarbonate.

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