Polyester catalyst-aid compound and application thereof in synthesis of food-grade biodegradable polyester

Abstract

The invention discloses a polyester catalyst and auxiliary agent compound and application thereof in synthesis of food-grade biodegradable polyester. The compound has a structure as shown in a formula I: [Mg < 2 + > nSa < + > xTib < + > y (OH) z] < + > [A-]. H2O / B, in the formula I, A <-> represents an anion, such as NO3 <->, HCO3 <-> or H2PO4 <->; b represents phosphides which are selected from phosphoric acid, phosphorous acid, pyrophosphoric acid and one or more than two of ester compounds of the phosphoric acid, the phosphorous acid and the pyrophosphoric acid; 2n / (ax + by) = 2, 2n + ax + by-z = 1, and n, a, b, x, y and z are all numbers greater than 0. The compound is used as a catalyst and an auxiliary agent to be applied to synthesis of PBS, and the prepared PBS not only has lower 1, 4-butanediol migration volume and oligomer migration volume, but also has extremely low acetaldehyde content, and meets the requirements of food contact materials specified by national food safety.

Description

Technical Field

[0001] The invention belongs to the field of polyester, and in particular relates to a polyester catalyst@auxiliary agent complex and application thereof in synthesizing food-grade biodegradable polyester. Background Art

[0002] With the awakening of people's awareness of ecological environmental protection, biodegradable polyesters such as polybutylene succinate (PBS), polyglycolic acid (PGA), polylactic acid (PLA) and the like have been widely studied. Among them, PBS has received great attention from the materials industry due to its low cost and good biodegradability. Since Showa Polymer Co., Ltd. of Japan developed the technology of preparing high molecular weight PBS by isocyanate chain extension, PBS has entered people's field of vision as a polymer material. In 2003, Mitsubishi Chemical of Japan built a 3,000 tons / year production line and put into use PBS products with high molecular weight without using chain extenders. In 2010, Anqing Hexing Chemical built my country's first large-scale 10,000-ton PBS production line, and Fuxin Pharmaceutical also built a 10,000-ton production line in the same year. In 2020, the global PBS market size reached 1.3 billion yuan, and it is expected to reach 3 billion yuan in 2026. The mass production of PBS will drive research in its application fields.

[0003] The thermodynamic properties of PBS reach or partially exceed those of non-degradable traditional plastics, and can replace traditional plastics and be applied to agricultural mulch, medical equipment, packaging containers and other fields. However, to apply PBS to fields related to medical treatment and food, it is also necessary to optimize the performance of PBS to meet the special requirements of medical treatment, food and other fields. The national food safety standard stipulates that materials or related products in contact with food have strict requirements for the migration and precipitation of additives and specific substances. Once the standard is exceeded or unapproved substances are used, major food safety issues will be caused. The national food safety standard has put forward restrictive requirements for the amount of additives used, specific migration limit or maximum residual amount, specific migration total limit and other provisions, special restrictions on metal elements, etc. In the generation process of PBS, due to the occurrence of thermal oxidation degradation side reactions, incomplete reaction of butanediol and other reasons, its specific migration amount, aldehyde content and the like are often not up to standard. CN 117430923A proposes to reduce the content of oligomers in polyester products to meet the requirements of food-grade polyester by extracting one or more solvents in water, methanol, ethanol, sodium chloride aqueous solution, drying and other purification processes, but this process is complicated to operate and is not conducive to the requirements of industrial amplification. CN 115197402 discloses polyester synthesized based on acid removal, which meets food grade requirements. However, excessive succinic acid or succinic anhydride causes serious corrosion to the reaction equipment, so expensive special equipment such as Hastelloy, polytetrafluoroethylene, and ceramics must be used. In addition, it cannot be completely removed due to its high boiling point.

[0004] Therefore, how to solve the problems that the migration amounts of 1,4-butanediol, oligomers and aldehyde substances in PBS products are relatively high and cannot meet the requirements of food-grade plastics has become a technical problem to be urgently solved in this field. Summary of the Invention

[0005] To improve the above technical problems, the present invention provides a complex having the structure shown in Formula I, which is used as a catalyst @ promoter (i.e., having the dual functions of a catalyst and a promoter) in the synthesis of PBS. The prepared PBS not only has relatively low migration amounts of 1,4-butanediol and oligomers, but also has an extremely low acetaldehyde content (not exceeding 0.5 ppm, relative to PBS), meeting the requirements of national food safety regulations for food contact materials.

[0006] The complex provided by the present invention has the structure shown in Formula I:

[0007] [Mg 2+ n Sn a+ x Ti b+ y (OH) z + [A - ·H2O / B Formula I

[0008] Wherein, A - represents an anion, such as NO3 - , HCO3 - or H2PO4 - ;

[0009] B represents a phosphide, such as selected from one or more of phosphoric acid, phosphorous acid, pyrophosphoric acid, and ester compounds of the above substances;

[0010] 2n / (ax + by) = 2, 2n + ax + by - z = 1, and n, a, b, x, y, and z are all numbers greater than 0.

[0011] According to an embodiment of the present invention, 0 < n < 1, for example, n = 2 / 3.

[0012] According to an embodiment of the present invention, a = b, for example, a = b = 4.

[0013] According to an embodiment of the present invention, x = y, for example, x = y = 1 / 6.

[0014] According to an embodiment of the present invention, when n = 2 / 3, a = b = 4, and x = y = 1 / 6, z = 2, that is, the complex shown in Formula I is [Mg 2+ 2 / 3 Sn​4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [A - ]·H2O / B.

[0015] According to an embodiment of the present invention, the ester compound can be selected from one or more of monophosphate, diester and triester, for example, selected from triester, exemplarily selected from one or more of trimethyl phosphate, tributyl phosphate and triethyl phosphate.

[0016] According to an embodiment of the present invention, [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·The mass ratio of H2O to B is (20-150):1, for example (30-130):1, exemplified by 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1 or 120:1.

[0017] According to an embodiment of the present invention, the composite is composed of [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·H2O and B are mixed according to the above mass ratio.

[0018] According to an exemplary embodiment of the present invention, the complex is [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / trimethyl phosphate, [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / tributyl phosphate, [Mg 2+ 2 / 3 Sn4 + 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / triethyl phosphate, [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphoric acid or [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphorous acid.

[0019] The present invention also provides the use of the above-mentioned complex as a catalyst / auxiliary agent in the preparation of PBS.

[0020] According to an embodiment of the present invention, the PBS is food grade PBS.

[0021] The present invention also provides a method for preparing the above-mentioned composite, comprising the following steps:

[0022] (1) A titanium compound, a tin compound and a magnesium salt are coprecipitated to form a layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·H2O;

[0023] (2) The layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ] · H2O and B are mixed to obtain the composite;

[0024] Wherein, A, B, n, a, b, x, y and z are all as defined above.

[0025] According to an embodiment of the present invention, the titanium compound may be a tetravalent titanium compound, such as one or more of titanium tetrachloride and titanium sulfate.

[0026] According to an embodiment of the present invention, the tin compound may be a tetravalent tin compound, such as one or more of tin tetrachloride and tin isopropoxide.

[0027] According to an embodiment of the present invention, the magnesium salt may be - A magnesium salt such as magnesium nitrate, magnesium dihydrogen phosphate or magnesium bicarbonate.

[0028] According to an embodiment of the present invention, the ratio of the magnesium salt, the titanium compound and the tin compound can satisfy the formula I Mg 2+ Sn 4+ and Ti 4+ molar ratio.

[0029] According to an embodiment of the present invention, the reaction conditions of the coprecipitation include:

[0030] Alkaline conditions, reaction temperature 90-150° C., and / or reaction time 3-10 h.

[0031] According to an embodiment of the present invention, the blending conditions include:

[0032] The layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ] The mass ratio of H2O to B is (20-150):1, for example (30-130):1, exemplified by 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1 or 120:1;

[0033] Reaction temperature 30~60℃;

[0034] and / or, stirring the reaction for 1 to 6 hours.

[0035] The present invention also provides a catalyst promoter comprising the composite.

[0036] The present invention also provides a catalyst, comprising the above-mentioned composite or catalyst aid.

[0037] The present invention also provides a PBS prepared from the above-mentioned composite, catalyst adjuvant or catalyst.

[0038] According to an embodiment of the present invention, the PBS has at least one or two or more of the following properties:

[0039] (a) Melt index is 14 to 25 g / 10 min;

[0040] (b) the oligomer content does not exceed 1%, preferably does not exceed 0.5%, and more preferably does not exceed 0.1%;

[0041] (c) the acetaldehyde content is not more than 1.5 ppm, preferably not more than 1 ppm, and more preferably not more than 0.5 ppm;

[0042] (d) The migration amount of 1,4-butanediol in acetic acid, aqueous, ethanol-containing and oil-containing foods meets the national food safety standard GB31604.51-2021.

[0043] According to an embodiment of the present invention, the weight average molecular weight of the oligomer is 5500-15000.

[0044] According to an embodiment of the present invention, the PBS is food grade PBS.

[0045] The present invention also provides a method for preparing the PBS, and the PBS is prepared from the complex.

[0046] According to an embodiment of the present invention, the preparation method of the PBS comprises:

[0047] (i) the above-mentioned composite is loaded into a tubular fixed bed reactor, and the preheated blend of 1,4-butanediol and dimethyl succinate enters the tubular fixed bed reactor for transesterification reaction; the generated methanol vapor is collected by condensation, and the generated oligomers are circulated into the fixed bed reactor again until no methanol is generated (at this time, the transesterification rate is greater than 95%, and the product molecular weight distribution is less than 1.5);

[0048] For example, the molar ratio of 1,4-butanediol to dimethyl succinate is (1-1.3):1;

[0049] For example, the temperature of the preheated blend is 50-60°C;

[0050] For example, the temperature of the transesterification reaction is 160-180°C;

[0051] (ii) introducing the product obtained in step (i) and the above-mentioned complex into a polymerization reactor together, and subjecting the mixture to polycondensation reaction to obtain the PBS;

[0052] For example, the mass ratio of the catalyst@auxiliary agent complex to the product obtained in step (i) is (0.1-5):100, preferably (0.5-2):100;

[0053] For example, the polycondensation reaction is carried out at 220 to 240°C.

[0054] Beneficial Effects

[0055] The present invention provides a complex having a structure shown in Formula I, which is used as a catalyst / auxiliary agent in the synthesis of PBS. The prepared PBS not only has low 1,4-butanediol migration amount and oligomer migration amount, but also has extremely low acetaldehyde content, meeting the requirements for food contact materials stipulated in national food safety regulations. DETAILED DESCRIPTION

[0056] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0057] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0058] Example 1

[0059] Embodiment 1 of the present invention provides a food-grade PBS, and the specific preparation process and test results are as follows:

[0060] 1. [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·Preparation of H2O / trimethyl phosphate complex:

[0061] Under nitrogen protection, 2 mol Mg(NO3)2, 1 mol SnCl4, and 1 mol TiCl4 were added to a flask containing 8 mol sodium hydroxide aqueous solution, stirred at 200 rpm, and reacted at 120°C for 6 hours. The reaction solution was centrifuged at 1000 rpm / min for 5 minutes, and the obtained white precipitate was washed with water and ethanol respectively and centrifuged again at 1000 rpm / min for 5 minutes to obtain a white precipitate, which is the layered metal hydroxide [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O. Finally [Mg 2+ 2 / 3 Sn4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O and trimethyl phosphate were reacted in a methanol solution at a mass ratio of 100:1, stirred at 50°C and 200 rpm for 2 hours, and then centrifuged to obtain a complex.

[0062] 2. Synthesis of PBS:

[0063] [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / trimethyl phosphate composite solid particles are used as catalyst@auxiliary agents, and are loaded into a tubular fixed bed reactor in a 3*3mm column with a loading amount of 5g. 1,4-Butanediol (BDO) and dimethyl succinate (DMS) are mixed at a molar ratio of 1.1:1 and preheated at 50°C. Then, they are fed into the fixed bed reactor from bottom to top through a feed pump at 5mL / min to undergo an ester exchange reaction at 160°C. The generated methanol vapor is collected by condensation, and the generated oligomers are recycled into the fixed bed reactor again until no methanol is generated. At this time, the ester exchange rate is 95%, and the molecular weight distribution of the product is 1.2. Finally, the product is mixed with [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / trimethyl phosphate (0.1% of the product mass) was introduced into a polymerization reactor, and polycondensation was carried out at 240°C and 50Pa. The reaction was carried out for 4 hours to obtain a PBS product.

[0064] The PBS prepared above was tested using the following test method:

[0065] 1. Determination of melt index: refer to GB / T 30294-2013, test at 190℃ and 2.16kg load;

[0066] 2. Determination of the migration amount of 1,4-butanediol; Referring to GB 31604.51-2021, four food simulants were selected, namely, the acidic food simulant was 4% acetic acid by volume, and the test conditions were 70°C, 2h; the aqueous food simulant was 10% ethanol by volume; the ethanol-containing food (ethanol content > 50%, volume fraction) food simulant was 95% ethanol, and the test conditions were 60°C, 2h; the oil-containing food simulant was isooctane, and the test conditions were 40°C, 30min; refer to Section 6.1 to calculate the migration amount of 1,4-butanediol.

[0067] 3. Determination of oligomer (weight average molecular weight 5500-15000) content: Accurately weigh a certain amount of sample and dissolve it with phenol-tetrachloroethane at a mass ratio of 1:1. The dissolved sample is tested by sol-gel permeation chromatography (GPC), and the mobile phase is chromatographic grade chloroform;

[0068] 4. Test of acetaldehyde content: Referring to GB / T 17931-2018, the residual acetaldehyde content in the PBS sample was determined by headspace chromatography according to the standard. The sample was crushed into powder and placed in a closed container at a certain temperature, and the sample released residual acetaldehyde. After reaching equilibrium, the gas part in the upper part of the closed container was introduced into the gas chromatography column to separate acetaldehyde from other components, and detected by a hydrogen flame ionization detector, and the acetaldehyde content released in the sample was quantitatively calculated by the external standard method.

[0069] The PBS prepared in this example was tested to have a melt index of 15.30 g / 10 min; the migration of 1,4-butanediol in the four simulants was not detected; the oligomer content was 0.07%; and the acetaldehyde content was 0.5 ppm.

[0070] Example 2

[0071] Embodiment 2 of the present invention provides a food-grade PBS, and the specific preparation process and test results are as follows:

[0072] 1. [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]· Preparation of H2O / tributyl phosphate complex:

[0073] Under nitrogen protection, 2 mol Mg(NO3)2, 1 mol SnCl4, and 1 mol TiCl4 were added to a flask containing 8 mol sodium hydroxide aqueous solution, stirred at 200 rpm, and reacted at 120°C for 6 hours. The reaction solution was centrifuged at 1000 rpm / min for 5 minutes, and the obtained white precipitate was washed with water and ethanol respectively and centrifuged again at 1000 rpm / min for 5 minutes to obtain a white precipitate, which is the layered metal hydroxide [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O. Finally [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O and tributyl phosphate were reacted in a butanol solution at a mass ratio of 100:1, stirred at 50°C and 200 rpm for 2 h, and then centrifuged to obtain a complex.

[0074] 2. Synthesis of PBS:

[0075] [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / tributyl phosphate was used as a catalyst@auxiliary compound, and loaded into a tubular fixed bed reactor in a 3*3mm column with a loading amount of 5g. 1,4-Butanediol (BDO) and dimethyl succinate (DMS) were mixed at a molar ratio of 1.2:1 and preheated at 50°C. The mixture was fed from bottom to top through a feed pump at 5mL / min into the fixed bed reactor at 160°C for transesterification. The generated methanol vapor was collected by condensation, and the generated oligomers were recycled into the fixed bed reactor again until no methanol was generated. At this time, the transesterification rate was 96%, and the molecular weight distribution of the product was 1.4. Finally, the product was mixed with [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 -]·H2O / tributyl phosphate (0.2% of the product mass) was introduced into a polymerization reactor and polycondensed at 230°C and 50Pa for 4 hours to obtain a PBS product.

[0076] The PBS prepared in this example was tested by the test method of Example 1: the melt index of the PBS prepared in this example was 18.33 g / 10 min; the migration of 1,4-butanediol in the four simulants was undetectable; the oligomer content was 0.05%; and the acetaldehyde content was 0.4 ppm.

[0077] Example 3

[0078] Embodiment 3 of the present invention provides a food-grade PBS, and the specific preparation process and test results are as follows:

[0079] 1. [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]· Preparation of H2O / triethyl phosphate complex:

[0080] Under nitrogen protection, 2 mol Mg(NO3)2, 1 mol SnCl4, and 1 mol TiCl4 were added to a flask containing 8 mol sodium hydroxide aqueous solution, stirred at 200 rpm, and reacted at 120°C for 6 hours. The reaction solution was centrifuged at 1000 rpm / min for 5 minutes, and the obtained white precipitate was washed with water and ethanol respectively and centrifuged again at 1000 rpm / min for 5 minutes to obtain a white precipitate, which is the layered metal hydroxide [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O. Finally [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O and triethyl phosphate were reacted in a butanol solution at a mass ratio of 90:1, stirred at 50°C and 200 rpm for 2 h, and then centrifuged to obtain a complex.

[0081] 2. Synthesis of PBS:

[0082] [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / triethyl phosphate was used as a catalyst@auxiliary agent complex, which was loaded into a tubular fixed bed reactor in a 3*3mm column with a loading amount of 5g. 1,4-Butanediol (BDO) and dimethyl succinate (DMS) were mixed at a molar ratio of 1.2:1 and preheated at 50°C. The mixture was fed from bottom to top through a feed pump at 5mL / min into the fixed bed reactor at 160°C for transesterification reaction. The generated methanol vapor was collected by condensation, and the generated oligomers were circulated into the fixed bed reactor again until no methanol was generated. At this time, the transesterification rate was 96%, and the molecular weight distribution of the product was 1.4. Finally, the product was mixed with [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / triethyl phosphate (0.1% of the product mass) was introduced into a polymerization reactor and polycondensed at 230°C and 50Pa for 4 hours to obtain a PBS product.

[0083] The PBS prepared in this example was tested by the test method of Example 1: the melt index of the PBS prepared in this example was 16.89 g / 10 min; the migration of 1,4-butanediol in the four simulants was undetectable; the oligomer content was 0.08%; and the acetaldehyde content was 0.5 ppm.

[0084] Example 4

[0085] Embodiment 4 of the present invention provides a food-grade PBS, and the specific preparation process and test results are as follows:

[0086] 1. [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]· Preparation of H2O / phosphoric acid complex:

[0087] Under nitrogen protection, 2 mol Mg(NO3)2, 1 mol Sn(CH3COO)4, and 1 mol Ti(SO4)2 were added into a flask containing 8 mol sodium hydroxide aqueous solution, stirred at 200 rpm, and reacted at 120°C for 6 hours. The reaction solution was centrifuged at 1000 rpm / min for 5 minutes, and the obtained white precipitate was washed with water and ethanol respectively and centrifuged again at 1000 rpm / min for 5 minutes to obtain a white precipitate, which is the layered metal hydroxide [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O. Finally [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O and phosphoric acid are reacted in an aqueous solution at a mass ratio of 100:1, stirred at 50°C and 200 rpm for 2 hours, and then centrifuged to obtain a complex.

[0088] 2. Synthesis of PBS:

[0089] [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphoric acid was used as a catalyst@auxiliary agent complex, loaded into a tubular fixed bed reactor in a 3*3mm column with a loading amount of 5g. 1,4-Butanediol (BDO) and dimethyl succinate (DMS) were mixed at a molar ratio of 1.2:1 and preheated at 50°C. The mixture was fed from bottom to top through a feed pump at 4mL / min into the fixed bed reactor at 170°C for transesterification. The generated methanol vapor was collected by condensation, and the generated oligomers were circulated into the fixed bed reactor again until no methanol was generated. At this time, the transesterification rate was 96% and the molecular weight distribution of the product was 1.5. Finally, the product was mixed with [Mg 2+ 2 / 3Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 -]·H2O / phosphoric acid (0.1% of the product mass) was introduced into a polymerization reactor, and polycondensation was carried out at 230°C and 50Pa. The reaction was performed for 5 hours to obtain a PBS product.

[0090] The PBS prepared in this example was tested by the test method of Example 1: the melt index of the PBS prepared in this example was 14.67 g / 10 min; the migration of 1,4-butanediol in the four simulants was undetectable; the oligomer content was 0.02%; and the acetaldehyde content was 0.3 ppm.

[0091] Example 5

[0092] Embodiment 5 of the present invention provides a food-grade PBS, and the specific preparation process and test results are as follows:

[0093] 1. [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]· Preparation of H2O / phosphorous acid complex:

[0094] Under nitrogen protection, 2 mol Mg(NO3)2, 1 mol Sn(CH3COO)4, and 1 mol Ti(SO4)2 were added into a flask containing 8 mol sodium hydroxide aqueous solution, stirred at 200 rpm, and reacted at 120°C for 6 hours. The reaction solution was centrifuged at 1000 rpm / min for 5 minutes, and the obtained white precipitate was washed with water and ethanol respectively and centrifuged again at 1000 rpm / min for 5 minutes to obtain a white precipitate, which is the layered metal hydroxide [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O. Finally [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O and phosphorous acid are reacted in an aqueous solution at a mass ratio of 60:1, stirred at 50°C and 200 rpm for 2 hours, and then centrifuged to obtain a complex.

[0095] 2. Synthesis of polybutylene succinate:

[0096] [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphorous acid as catalyst@auxiliary agent complex, loaded into a tubular fixed bed reactor in a 3*3mm column with a loading amount of 5g, 1,4-butanediol (BDO) and dimethyl succinate (DMS) were mixed at a molar ratio of 1.2:1 and preheated at 50°C, and then fed into the fixed bed reactor from bottom to top through a feed pump at 4mL / min to undergo ester exchange reaction at 170°C. The generated methanol vapor was collected by condensation, and the generated oligomers were circulated into the fixed bed reactor again until no methanol was generated. At this time, the ester exchange rate was 95.5%, and the molecular weight distribution of the product was 1.2. Finally, the product was mixed with [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphorous acid (0.1% of the product mass) was introduced into a polymerization reactor and polycondensed at 220°C and 50Pa for 4 hours to obtain a PBS product.

[0097] The PBS prepared in this example was tested by the test method of Example 1: the melt index of the PBS prepared in this example was 20.60 g / 10 min; the migration of 1,4-butanediol in the four simulants was undetectable; the oligomer content was 0.01%; and the acetaldehyde content was 0.4 ppm.

[0098] Comparative Example 1

[0099] Under nitrogen protection, 0.01 mol of tetrabutyl titanate, 2.4 mol of 1,4-butanediol and 2 mol of dimethyl succinate were added to a kettle reactor at 300 rpm, the temperature was raised to 170°C for reaction for 2 h, until no methanol was produced, and then the temperature was gradually raised to 230°C and 50 Pa for reaction for 4 h to stop the reaction and prepare PBS.

[0100] The PBS prepared in this comparative example was tested by the testing method of Example 1: the melt index was 15.10 g / 10 min; the migration amounts of 1,4-butanediol in acidic food simulants, aqueous food simulants, ethanol-containing food simulants, and oil-containing food simulants were 43 ppm, 24 ppm, 49 ppm, and 22 ppm, respectively; the oligomer content was 1.3%; and the acetaldehyde content was 1.7 ppm.

[0101] Comparative Example 2

[0102] Under nitrogen protection, 0.02 mol of tetraethyl titanate, 2.2 mol of 1,4-butanediol and 2 mol of dimethyl succinate were added to a kettle reactor at 400 rpm, the temperature was raised to 180°C and reacted for 2 h until no methanol was produced, and then the temperature was gradually raised to 240°C and 50 Pa for 4 h to stop the reaction and prepare PBS.

[0103] The PBS prepared in this comparative example was tested by the testing method of Example 1: the melt index was 13.11 g / 10 min; the migration amounts of 1,4-butanediol in acidic food simulants, aqueous food simulants, ethanol-containing food simulants, and oil-containing food simulants were 33 ppm, 30 ppm, 46 ppm, and 38 ppm, respectively; the oligomer content was 1.6%; and the acetaldehyde content was 4.8 ppm.

[0104] Comparative Example 3

[0105] Only [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O, and a synthesis experiment of PBS was carried out. Except that trimethyl phosphate was not added for blending, other steps were the same as those in Example 1.

[0106] The PBS prepared in this comparative example was tested by the testing method of Example 1: the melt index was 37 g / 10 min; the migration amounts of 1,4-butanediol in acidic food simulants, aqueous food simulants, ethanol-containing food simulants, and oil-containing food simulants were 4 ppm, 7 ppm, 3 ppm, and undetectable, respectively; the oligomer content was 0.2%; and the acetaldehyde content was 0.9 ppm.

[0107] Comparative Example 4

[0108] Compared with Example 1, except that [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O preparation, except that trimethyl phosphate is used for the synthesis of PBS, the other steps are the same, resulting in the phenomenon that PBS does not polymerize, so no PBS product can be obtained.

[0109] Table 1 Parameters of polybutylene succinate prepared in Examples 1-5 and Comparative Examples 1 and 2

[0110]

[0111] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A composite, characterized in that The complex has a structure as shown in Formula I: [Mg 2+ n Sn a+ x Ti b+ y (OH) z + [A - ·H2O / B Formula I​ Among them, A - Represents anions, such as NO3 - 、HCO3 - or H2PO4 - ; B represents a phosphide, for example, one or more selected from phosphoric acid, phosphorous acid, pyrophosphoric acid, and ester compounds of the above substances; 2n / (ax+by)=2, 2n+ax+by-z=1, n, a, b, x, y and z are all numbers greater than 0.

2. The composite according to claim 1, characterized in that 0<n<1； and / or, a=b; and / or, x=y; Preferably, when n=2 / 3, a=b=4 and x=y=1 / 6, z=2, that is, the complex shown in formula I is [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4 + 1 / 6 (OH)2] + [A - ]·H2O / B; And / or, the ester compound is selected from one or more of monoesters, diesters and triesters of phosphate, for example, selected from triesters of phosphate, such as one or more of trimethyl phosphate, tributyl phosphate and triethyl phosphate.

3. The composite according to claim 1, characterized in that [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·The mass ratio of H2O to B is (20~150):

1.

4. The composite according to claim 1, characterized in that The complex is [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / trimethyl phosphate, [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / tributyl phosphate, [Mg 2+ 2 / 3 Sn 4 + 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / triethyl phosphate, [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphoric acid or [Mg 2+ 2 / 3 Sn 4+ 1 / 6 Ti 4+ 1 / 6 (OH)2] + [NO3 - ]·H2O / phosphorous acid.

5. Use of the complex according to any one of claims 1 to 4 as a catalyst / auxiliary agent in the preparation of PBS.

6. The method for preparing the composite according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: (1) A titanium compound, a tin compound and a magnesium salt are coprecipitated to form a layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·H2O; (2) The layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·H2O is mixed with B to obtain the composite.

7. The preparation method according to claim 6, characterized in that: The reaction conditions of the coprecipitation include: alkaline conditions, a reaction temperature of 90 to 150° C., and / or a reaction time of 3 to 10 hours. Preferably, the blending conditions include: The layered metal hydroxide [Mg 2+ n Sn a+ x Ti b+ y (OH) z ] + [A - ]·The mass ratio of H2O to B is (20-150):1; the reaction temperature is 30-60°C; and / or, the reaction is stirred for 1-6 hours.

8. A PBS, characterized in that: The PBS has at least one or two or more of the following properties: (a) Melt index is 14 to 25 g / 10 min; (b) the oligomer content does not exceed 1%, preferably does not exceed 0.5%, and more preferably does not exceed 0.1%; (c) the acetaldehyde content is not more than 1.5 ppm, preferably not more than 1 ppm, and more preferably not more than 0.5 ppm; (d) The migration amount of 1,4-butanediol in acetic acid, water, ethanol and oil-containing foods meets the national food safety standard GB 31604.51-2021; Preferably, the weight average molecular weight of the oligomer is 5500 to 15000; Preferably, the PBS is prepared from the complex according to any one of claims 1-4.

9. The method for preparing PBS according to claim 8, characterized in that: The PBS is prepared from the complex according to any one of claims 1 to 4.

10. The preparation method according to claim 9, characterized in that: The preparation method of the PBS comprises: (i) the composite is loaded into a tubular fixed bed reactor, and the preheated mixture of 1,4-butanediol and dimethyl succinate enters the tubular fixed bed reactor for transesterification reaction; the generated methanol vapor is collected by condensation, and the generated oligomers are circulated into the fixed bed reactor again until no methanol is generated; (ii) introducing the product obtained in step (i) and the complex into a polymerization reactor together, and performing polycondensation reaction to obtain the PBS.

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