Bio-based composite plasticizer as well as preparation method and application thereof

Abstract

The invention relates to a bio-based composite plasticizer and a preparation method and application thereof, and solves the technical problems that the existing bio-based plasticizer is high in energy consumption, easy to cause environmental pollution and unsatisfactory in plasticizing effect, the bio-based composite plasticizer contains citrate, and also contains 0.68-23.85% by mass of aconitic acid ester and 0.1-0.5% by mass of fumarate, the mass percent of the fumarate is 1.38%-8.8%, and the balance is the citrate. The method can be widely applied to the field of preparation of high polymer materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer chemical industry, in particular to a bio-based composite plasticizer and a preparation method and application thereof. BACKGROUND

[0002] At present, the mainstream production method of citric acid in industry is microbial fermentation method, usually using microorganism strains such as Aspergillus niger to ferment to obtain citric acid fermentation liquor, and then using calcium salt method or other methods to crystallize to obtain citric acid product. For example, a preparation method of citric acid or sodium citrate is disclosed in Chinese patent CN1034023C; a method for extracting and refining citric acid from citric acid fermentation liquor is disclosed in Chinese patent CN101781190B.

[0003] In the traditional process, the specific process for preparing citric acid from fermentation liquor includes the following steps: adding calcium hydroxide or calcium carbonate to the citric acid fermentation liquor to obtain calcium citrate precipitate, separating the precipitate, and then acidifying with sulfuric acid to obtain citric acid liquor, and finally obtaining citric acid product through evaporation, concentration, crystallization and drying.

[0004] Through the above steps, it can be found that there are many problems in the process of crystallizing and purifying citric acid by calcium salt method: (1) high energy consumption: repeated heating / cooling is required to control the temperature of the crystallization environment, the steam consumption is large, and the energy consumption of the drying process is high (more than 40% of the total energy consumption); (2) large amount of solid waste: sulfuric acid is added to displace and separate citric acid from calcium citrate solid, but at the same time, calcium sulfate waste (gypsum) is generated. Theoretically, 1.34 tons of gypsum will be generated for every ton of citric acid product produced. Due to the influence of impurities and moisture, the amount of gypsum generated is larger in actual production. The common practice at present is to landfill these gypsums, which not only occupies a large amount of land resources but also has high pollution risk, brings great environmental pressure, and the cost of solid waste landfill is high (about 300 yuan / ton); (3) raw material waste: the by-products such as aconitic acid, fumaric acid, malic acid, oxalic acid and gluconic acid in the fermentation liquor are removed as impurities in the traditional process, which is not effectively utilized, causing resource waste.

[0005] On the other hand, the traditional citric acid ester production process also has certain limitations. A large amount of manpower and material resources are consumed for adding citric acid, efficient and automated production is difficult to achieve, and a large amount of dust is generated, which is extremely unfriendly to the environment and operating personnel. SUMMARY

[0006] The present application provides a bio-based composite plasticizer which can effectively reduce energy consumption, reduce the generation of solid waste and has good plasticizing effect, and a preparation method and application thereof, in order to solve the technical problems of high energy consumption, easy environmental pollution and unsatisfactory plasticizing effect of existing bio-based plasticizers.

[0007] To this end, the present application provides a kind of composite bio-based plasticizer, it contains citric acid ester, also contains aconitic acid ester and fumaric acid ester, the mass percentage content of aconitic acid ester is 0.68%~23.85%, the mass percentage content of fumaric acid ester is 1.38%~8.8%, the rest is citric acid ester.

[0008] Preferably, citric acid ester is one of tri-n-butyl citrate, tri-octyl citrate, triethyl citrate, tri-decyl citrate or tributyl citrate or a mixture of two or more thereof; tributyl citrate is one of triisobutyl citrate, diisobutyl-n-butyl citrate, mono-isobutyl di-n-butyl citrate, tri-n-butyl citrate or a mixture of two or more thereof.

[0009] Preferably, aconitic acid ester is one of tri-n-butyl aconitate, tri-octyl aconitate, triethyl aconitate, tri-decyl aconitate, tri-butyl aconitate or a mixture of two or more thereof; tri-butyl aconitate is one of triisobutyl aconitate, diisobutyl-n-butyl aconitate, mono-isobutyl di-n-butyl aconitate, tri-n-butyl aconitate or a mixture of two or more thereof.

[0010] Preferably, fumaric acid ester is one of di-n-butyl fumarate, di-octyl fumarate, diethyl fumarate, di-decyl fumarate, di-butyl fumarate or a mixture of two or more thereof; di-butyl fumarate is one of diisobutyl fumarate, mono-isobutyl-n-butyl fumarate, di-n-butyl fumarate or a mixture of two or more thereof.

[0011] The present application also provides a preparation method of the composite bio-based plasticizer, comprising the following steps: A: filtering out mycelium, raw material residue and incompletely dissolved metabolites from citric acid fermentation liquor, and then pouring into a reactor according to the mass ratio of acid to alcohol of 1:(1.08~2.88), continuously stirring, and adding a catalyst to perform a heating reaction; the mass percentage content of acid in the citric acid fermentation liquor is 35~40%; the acid comprises aconitic acid with a mass percentage of 0.8%~25%, fumaric acid with a mass percentage of 2%~7.1%, and the rest is citric acid; B: when the esterification reaction stops, an alkaline solution is added for alkaline washing, and after separating the alkaline washing wastewater, the crude ester after water washing is further washed with pure water to remove the catalyst, incompletely reacted acid and salt generated by neutralization in the reaction system; C: the crude ester after water washing is purified by rectification and then decolorized by activated carbon, and the finished product is obtained after filtration; the reactor can be a reaction kettle type reactor, a tower type reactor, a fixed bed reactor, a pipe type reactor, a micro-channel reactor, etc.

[0012] Preferably, in step B, the heating reaction temperature is not more than 165℃.

[0013] Preferably, in step B, the alcohol is a monohydric alcohol.

[0014] Preferably, the alcohol in step B is a C1-C16 alcohol.

[0015] Preferably, in step B, the catalyst is p-toluenesulfonic acid or methyl sulfonic acid; and in step C, the basic solution is a NaOH solution.

[0016] The application also provides a use of the composite bio-based plasticizer in the preparation of a PVC product.

[0017] The application has the following beneficial effects:

[0018] (1) The application completely skips the crystallization and drying steps in the traditional extraction of citric acid process, and directly uses the citric acid fermentation liquor and alcohol to perform an esterification reaction to prepare citric acid ester, thereby greatly reducing the energy consumption in the production process of citric acid and reducing the generation of solid waste.

[0019] (2) The application fully utilizes the "impurities" such as aconitic acid and fumaric acid in the citric acid fermentation liquor, and reacts with alcohol to generate corresponding ester substances. Due to the excellent performance of aconitic acid ester and fumaric acid ester, the final product can have good processing performance in the downstream, and the bio-based plasticizer prepared has better stability, better aging resistance, and lower precipitation resistance compared with the citric acid ester plasticizer prepared from traditional pure citric acid, effectively improving the processing performance of the target product and increasing the product added value. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The PVC aging resistance test results of the plasticizer prepared in Example 1, Example 6, and Comparative Example 1 of the application are shown in the following figure.

[0021] Figure 2 The PVC aging resistance test results of the plasticizer prepared in Example 2, Example 7, and Comparative Example 2 of the application are shown in the following figure.

[0022] Figure 3 The PVC aging resistance test results of the plasticizer prepared in Example 3, Example 8, and Comparative Example 3 of the application are shown in the following figure.

[0023] Figure 4 The PVC aging resistance test results of the plasticizer prepared in Example 4, Example 9, and Comparative Example 4 of the application are shown in the following figure.

[0024] Figure 5 The PVC aging resistance test results of the plasticizer prepared in Example 5, Example 10, and Comparative Example 5 of the application are shown in the following figure. DETAILED DESCRIPTION

[0025] The application will be further described below with reference to the accompanying drawings and examples, so that those skilled in the art can easily implement the application.

[0026] The citric acid fermentation liquor used in the following examples was prepared by the method described in Chinese patents CN1034023C or CN101781190B.

[0027] The bio-based composite plasticizer prepared in the following examples of the application can be used in the preparation of PVC products, and its use method can refer to the method described in other bio-based plasticizers, such as Chinese patent CN102617887B.

[0028] Example 1

[0029] At normal temperature and pressure, 200.00 g of citric acid fermentation liquor (acid effective content about 40.00%, containing about 97.00% of citric acid, about 0.80% of aconitic acid, and about 2.00% of fumaric acid), 108.02 g of n-butanol, and 0.80 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and heated with stirring, with the highest reaction temperature controlled at 165℃. When the water output reached 142.50 g, the reaction was stopped by cooling. Then the crude ester was washed with 30.00 g of 2.00% NaOH solution, and after the alkali washing wastewater was separated, the crude product was washed with 30.00 g of pure water and the wastewater was separated. The crude product after water washing was subjected to vacuum distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 97.49% of citric acid tri-n-butyl ester, 0.68% of aconitic acid tri-n-butyl ester, and 1.38% of fumaric acid di-n-butyl ester.

[0030] Example 2

[0031] At normal temperature and pressure, 160.00 g of citric acid fermentation liquor (acid effective content about 40.00%, containing about 97.00% of citric acid, about 0.80% of aconitic acid, and about 2.00% of fumaric acid), 151.84 g of octanol, and 0.64 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and heated with stirring and vacuum operation of the reaction system, with the highest reaction temperature controlled at 150℃. When the water output reached 114.00 g, the reaction was stopped by cooling. Then the crude ester was washed with 33.00 g of 1.00% NaOH solution, and after the alkali washing wastewater was separated, the crude product was washed with 33.00 g of pure water and the wastewater was separated. The crude product after water washing was subjected to vacuum distillation (pressure ≤7 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 96.87% of citric acid tri-octyl ester, 0.79% of aconitic acid tri-octyl ester, and 1.87% of fumaric acid di-octyl ester.

[0032] Example 3

[0033] At normal temperature and pressure, 210.00 g of citric acid fermentation broth (acid effective content of about 40.00%, containing about 97.00% citric acid, about 0.80% aconitic acid, and about 2.00% fumaric acid), 120.85 g of anhydrous ethanol, and 0.84 g of concentrated sulfuric acid were added to a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device. The mixture was heated with stirring, and the highest reaction temperature was controlled at 140°C. New anhydrous ethanol was continuously added during the reaction, and an equal amount of ethanol and water mixture was simultaneously discharged through the reflux bottle. The water content in the discharged mixture was determined by a micro moisture meter. When the amount of discharged water reached 149.63 g, the reaction was stopped by cooling, and the excess ethanol was removed. Subsequently, the crude ester was washed with 19.50 g of 1.50% NaOH solution, and the waste water was separated. Then, the crude product was washed with 19.50 g of pure water, and the waste water was separated again. The washed crude product was subjected to vacuum distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 97.36% citric acid triethyl ester, 0.76% aconitic acid triethyl ester, and 1.40% fumaric acid diethyl ester.

[0034] Example 4

[0035] At normal temperature and pressure, 150.00 g of citric acid fermentation broth (acid effective content of about 40.00%, containing about 97.00% citric acid, about 0.80% aconitic acid, and about 2.00% fumaric acid), 173.01 g of decanol, and 0.60 g of p-toluenesulfonic acid were added to a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device. The mixture was heated with stirring and subjected to vacuum operation. The highest reaction temperature was controlled at 160°C. When the amount of discharged water reached 106.88 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 36.00 g of 1.00% NaOH solution, and the waste water was separated. Then, the crude product was washed with 36.00 g of pure water, and the waste water was separated again. The washed crude product was subjected to vacuum distillation (pressure ≤6 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 97.05% citric acid tridecyl ester, 1.02% aconitic acid tridecyl ester, and 1.48% fumaric acid didecyl ester.

[0036] Example 5

[0037] At normal temperature and pressure, 220.00 g of citric acid fermentation liquor (acid effective content about 40.00%, containing about 97.00% of citric acid, about 0.80% of aconitic acid, and about 2.00% of fumaric acid), 95.06 g of n-butanol, 23.77 g of isobutyl alcohol, and 0.88 g of p-toluene sulfonic acid are put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and heated with stirring, with the highest reaction temperature controlled at 165°C. When the water output reaches 156.76 g, the reaction is stopped by cooling. Then the crude ester is washed with 31.50 g of 2.00% NaOH solution, and after the waste water is separated, the crude product is washed with 31.50 g of pure water and the waste water is separated. The crude product after water washing is subjected to reduced pressure distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis shows that the target product contains 97.32% of tributyl citrate (containing triisobutyl citrate, diisobutyl-n-butyl citrate, isobutyl-n-dibutyl citrate, and tri-n-butyl citrate), 0.71% of tributyl aconitate (containing triisobutyl aconitate, diisobutyl-n-butyl aconitate, isobutyl-n-dibutyl aconitate, and tri-n-butyl aconitate), and 1.49% of dibutyl fumarate (containing diisobutyl fumarate, isobutyl-n-dibutyl fumarate, and di-n-butyl fumarate).

[0038] Example 6

[0039] At normal temperature and pressure, 220.00 g of citric acid fermentation liquor (acid effective content about 40.00%, containing about 97.00% of citric acid, about 0.80% of aconitic acid, and about 2.00% of fumaric acid), 95.06 g of n-butanol, 23.77 g of isobutyl alcohol, and 0.88 g of p-toluene sulfonic acid are put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and heated with stirring, with the highest reaction temperature controlled at 165°C. When the water output reaches 156.76 g, the reaction is stopped by cooling. Then the crude ester is washed with 31.50 g of 2.00% NaOH solution, and after the waste water is separated, the crude product is washed with 31.50 g of pure water and the waste water is separated. The crude product after water washing is subjected to reduced pressure distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis shows that the target product contains 97.32% of tributyl citrate (containing triisobutyl citrate, diisobutyl-n-butyl citrate, isobutyl-n-dibutyl citrate, and tri-n-butyl citrate), 0.71% of tributyl aconitate (containing triisobutyl aconitate, diisobutyl-n-butyl aconitate, isobutyl-n-dibutyl aconitate, and tri-n-butyl aconitate), and 1.49% of dibutyl fumarate (containing diisobutyl fumarate, isobutyl-n-dibutyl fumarate, and di-n-butyl fumarate).

[0040] Example 7

[0041] At normal temperature and pressure, 180.00 g of citric acid fermentation liquor (acid effective content about 35.00%, which contains about 67.00% of citric acid, about 25.00% of aconitic acid, and about 7.10% of fumaric acid), 149.46 g of octanol, and 0.63 g of p-toluenesulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device. The reaction system was heated and operated under reduced pressure, and the highest reaction temperature was controlled at 150°C. When the water output reached 134.72 g, the reaction was stopped by cooling. Then, the crude ester was washed with 32.25 g of 1.00% NaOH solution once, and after the alkali washing wastewater was separated, it was washed with 32.25 g of pure water once and the wastewater was separated. The crude product after water washing was subjected to reduced pressure distillation (pressure ≤7 kPa) to obtain the target product. Gas chromatography analysis showed that it contained 67.91% of citric acid trioctyl ester, 23.85% of aconitic acid trioctyl ester, and 7.74% of fumaric acid dioctyl ester.

[0042] Example 8

[0043] At normal temperature and pressure, 230.00 g of citric acid fermentation liquor (acid effective content about 35.00%, which contains about 67.00% of citric acid, about 25.00% of aconitic acid, and about 7.10% of fumaric acid), 115.82 g of anhydrous ethanol, and 0.81 g of concentrated sulfuric acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device. The reaction system was heated, and the highest reaction temperature was controlled at 140°C. New anhydrous ethanol was continuously added during the reaction, and an equal amount of ethanol and water mixture was simultaneously discharged through the reflux bottle. The water content in the discharged mixture was determined by a micro water meter. When the water output reached 172.15 g, the reaction was stopped by cooling and the excess ethanol was removed. Then, the crude ester was washed with 18.00 g of 1.50% NaOH solution once, and after the alkali washing wastewater was separated, it was washed with 18.00 g of pure water once and the wastewater was separated. The crude product after water washing was subjected to reduced pressure distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis showed that it contained 67.53% of citric acid triethyl ester, 23.24% of aconitic acid triethyl ester, and 8.80% of fumaric acid diethyl ester.

[0044] Example 9

[0045] At normal temperature and pressure, 160.00 g of citric acid fermentation liquor (acid effective content about 35.00%, which contains about 67.00% of citric acid, about 25.00% of aconitic acid, and about 7.10% of fumaric acid), 161.48 g of decyl alcohol, and 0.56 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and then stirred and heated, and the reaction system was operated under reduced pressure, with the highest reaction temperature controlled at 160°C; when the water output reached 119.75 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 34.50 g of 1.00% NaOH solution, and then washed with 34.50 g of pure water, and the waste water was separated; the crude product after water washing was subjected to reduced pressure distillation (pressure ≤ 6 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 68.03% of citric acid tri-decyl ester, 23.51% of aconitic acid tri-decyl ester, and 8.02% of fumaric acid di-decyl ester.

[0046] Example 10

[0047] At normal temperature and pressure, 230.00 g of citric acid fermentation liquor (acid effective content about 35.00%, which contains about 67.00% of citric acid, about 25.00% of aconitic acid, and about 7.10% of fumaric acid), 86.96 g of n-butyl alcohol, 21.74 g of isobutyl alcohol, and 0.81 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser tube, a reflux bottle, a thermometer, and a stirring device, and then stirred and heated, with the highest reaction temperature controlled at 165°C; when the water output reached 172.15 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 30.00 g of 2.00% NaOH solution, and then washed with 30.00 g of pure water, and the waste water was separated; the crude product after water washing was subjected to reduced pressure distillation (pressure ≤ 10 kPa) to obtain the target product. Gas chromatography analysis showed that the target product contained 68.24% of citric acid tri-butyl ester (which contained citric acid tri-isobutyl ester, citric acid di-isobutyl mono-n-butyl ester, citric acid mono-isobutyl di-n-butyl ester, and citric acid tri-n-butyl ester), 23.33% of aconitic acid tri-butyl ester (which contained aconitic acid tri-isobutyl ester, aconitic acid di-isobutyl mono-n-butyl ester, aconitic acid mono-isobutyl di-n-butyl ester, and aconitic acid tri-n-butyl ester), and 7.99% of fumaric acid di-butyl ester (which contained fumaric acid di-isobutyl ester, fumaric acid mono-isobutyl mono-n-butyl ester, and fumaric acid di-n-butyl ester).

[0048] Comparative Example 1

[0049] Under normal temperature and pressure, 150.00 g of anhydrous citric acid (purity 100.05%), 202.55 g of n-butanol, and 1.50 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device, and heated with stirring, with the highest reaction temperature controlled at 165°C. When the water output reached 42.20 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 51.00 g of a 2.00% NaOH solution, and after the alkali washing wastewater was removed, the crude product was washed with 51.00 g of pure water and the wastewater was removed. The crude product after washing was subjected to reduced pressure distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis showed that the content of tri-n-butyl citrate was 99.57%.

[0050] Comparative Example 2

[0051] Under normal temperature and pressure, 100.00 g of anhydrous citric acid (purity 100.05%), 237.24 g of octanol, and 1.00 g of p-toluene sulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device, and heated with stirring and reduced pressure operation, with the highest reaction temperature controlled at 150°C. When the water output reached 28.13 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 49.50 g of a 1.00% NaOH solution, and after the alkali washing wastewater was removed, the crude product was washed with 49.50 g of pure water and the wastewater was removed. The crude product after washing was subjected to reduced pressure distillation (pressure ≤7 kPa) to obtain the target product. Gas chromatography analysis showed that the content of trioctyl citrate was 99.12%.

[0052] Comparative Example 3

[0053] Under normal temperature and pressure, 140.00 g of anhydrous citric acid (purity 100.05%), 201.42 g of anhydrous ethanol, and 1.40 g of concentrated sulfuric acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device, and heated with stirring, with the highest reaction temperature controlled at 140°C. During the reaction, new anhydrous ethanol was continuously added, and an equal amount of ethanol and water mixture was simultaneously discharged through the reflux bottle. The water content in the discharged mixture was determined by a micro water meter. When the water output reached 39.38 g, the reaction was stopped by cooling and the excess ethanol was removed. Subsequently, the crude ester was washed with 31.50 g of a 1.50% NaOH solution, and after the alkali washing wastewater was removed, the crude product was washed with 31.50 g of pure water and the wastewater was removed. The crude product after washing was subjected to reduced pressure distillation (pressure ≤10 kPa) to obtain the target product. Gas chromatography analysis showed that the content of triethyl citrate was 99.52%.

[0054] Comparative Example 4

[0055] At normal temperature and pressure, 80.00 g of anhydrous citric acid (purity 100.05%), 230.68 g of decanol, and 0.80 g of p-toluenesulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device. The mixture was heated with stirring, and the reaction system was operated under reduced pressure. The highest reaction temperature was controlled at 160°C. When the water output reached 22.50 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 46.50 g of a 1.00% NaOH solution. After the alkali washing wastewater was removed, the crude product was washed with 46.50 g of pure water and the wastewater was removed. The crude product after water washing was subjected to reduced pressure distillation (pressure ≤ 6 kPa) to obtain the target product. Gas chromatography analysis showed that the content of citric acid tri-decyl ester was 99.34%.

[0056] Comparative Example 5

[0057] At normal temperature and pressure, 150.00 g of anhydrous citric acid (purity 100.05%), 162.04 g of n-butanol, 40.51 g of isobutyl alcohol, and 1.50 g of p-toluenesulfonic acid were put into a 500 mL three-necked flask equipped with an esterification tower, a condenser, a reflux bottle, a thermometer, and a stirring device. The mixture was heated with stirring, and the highest reaction temperature was controlled at 165°C. When the water output reached 42.20 g, the reaction was stopped by cooling. Subsequently, the crude ester was washed with 51.00 g of a 2.00% NaOH solution. After the alkali washing wastewater was removed, the crude product was washed with 51.00 g of pure water and the wastewater was removed. The crude product after water washing was subjected to reduced pressure distillation (pressure ≤ 10 kPa) to obtain the target product. Gas chromatography analysis showed that the content of citric acid ester reached 99.62% (containing citric acid tri-isobutyl ester, citric acid di-isobutyl-n-butyl ester, citric acid mono-isobutyl di-n-butyl ester, and citric acid tri-n-butyl ester).

[0058] Table 1: Extraction resistance data of Example 1, Example 6, and Comparative Example 1

[0059] % resistance to extraction with absolute ethanol Example 1 1.1241 Example 6 0.9125 Comparative Example 1 1.2726

[0060] Table 2: Extraction resistance data of Example 2, Example 7, and Comparative Example 2

[0061] % resistance to extraction with absolute ethanol Example 2 0.8634 Example 7 0.6781 Comparative Example 2 0.9056

[0062] Table 3: Extraction resistance data of Example 3, Example 8, and Comparative Example 3

[0063] % resistance to extraction with absolute ethanol Example 3 1.5367 Example 8 1.3125 Comparative Example 3 1.6684

[0064] Table 4: Extraction resistance data of Example 4, Example 9, and Comparative Example 4

[0065] % resistance to extraction with absolute ethanol Example 4 0.8223 Example 9 0.6681 Comparative Example 4 0.9157

[0066] Table 5: Extraction resistance data of Example 5, Example 10, Comparative Example 5

[0067] % resistance to extraction with absolute ethanol Example 5 1.1143 Example 10 0.9769 Comparative Example 5 1.2238

[0068] As can be seen from Examples 1-10, when the fermentation liquor is properly controlled to increase the production of aconitic acid and fumaric acid, the performance of the obtained product is significantly improved. In the traditional citric acid fermentation process, aconitic acid and fumaric acid are removed as impurities, and a large amount of by-product acid is wasted.

[0069] As can be seen from Comparative Examples 1-5, although the prepared citric acid has very high purity, the performance of the citric acid ester synthesized therefrom is not outstanding.

[0070] From the attached Figures 1 to 5 As can be seen, the aging resistance of the PVC product prepared using the bio-based composite plasticizer in Examples 1-10 is significantly improved.

[0071] The above description is only for the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the scope defined by the claims of the present application shall be within the scope of protection of the present application.

Claims

1. A composite bio-based plasticizer containing a citrate ester, characterized in that: It also contains aconitate and fumarate, wherein the mass percentage of the aconitate is 0.68% to 23.85%, the mass percentage of the fumarate is 1.38% to 8.8%, and the rest is citrate.

2. The composite bio-based plasticizer according to claim 1, characterized in that The citric acid ester is one of tri-n-butyl citrate, trioctyl citrate, triethyl citrate, tridecyl citrate or tributyl citrate, or a mixture of two or more thereof; the tributyl citrate is one of triisobutyl citrate, diisobutyl-n-butyl citrate, diisobutyl-n-butyl citrate or tri-n-butyl citrate, or a mixture of two or more thereof.

3. The composite bio-based plasticizer according to claim 1, characterized in that: The aconitate ester is one of tri-n-butyl aconitate, trioctyl aconitate, triethyl aconitate, tridecyl aconitate, tributyl aconitate, or a mixture of two or more thereof; the tributyl aconitate refers to one of triisobutyl aconitate, diisobutyl-n-butyl aconitate, diisobutyl-n-butyl aconitate, tri-n-butyl aconitate, or a mixture of two or more thereof.

4. The composite bio-based plasticizer according to claim 1, characterized in that The fumarate ester is one of di-n-butyl fumarate, dioctyl fumarate, diethyl fumarate, didecyl fumarate, dibutyl fumarate, or a mixture of two or more thereof; the dibutyl fumarate refers to one of diisobutyl fumarate, monoisobutyl-n-butyl fumarate, di-n-butyl fumarate, or a mixture of two or more thereof.

5. The method for preparing the composite bio-based plasticizer according to claim 1, wherein: Contains the following steps: A: Filter the citric acid fermentation broth to remove mycelium, raw material residue, and incompletely dissolved metabolites, and inject the broth into a reactor at an acid to alcohol mass ratio of 1:(1.08-2.88), continuously stir, add a catalyst, and heat to react; the citric acid fermentation broth contains 35-40% by weight of acid; the acid comprises 0.8-25% by weight of aconitic acid, 2-7.1% by weight of fumaric acid, and the remainder is citric acid; B: When the esterification reaction stops, add alkaline solution for alkaline washing. After separating the alkaline washing wastewater, further wash with pure water to remove the catalyst, unreacted acid and salt produced by neutralization in the reaction system; C: The crude ester after washing is distilled and purified, decolorized with activated carbon, and filtered to obtain the finished product.

6. The method for preparing the composite bio-based plasticizer according to claim 5, characterized in that: In the step B, the heating reaction temperature does not exceed 165°C.

7. The method for preparing the composite bio-based plasticizer according to claim 5, characterized in that: The alcohol in step B is a monohydric alcohol.

8. The method for preparing the composite bio-based plasticizer according to claim 6, characterized in that: The alcohol in step B is C1-C16 alcohol.

9. The method for preparing the composite bio-based plasticizer according to claim 5, characterized in that: In the step B, the catalyst is p-toluenesulfonic acid or methanesulfonic acid; in the step C, the alkaline solution is NaOH solution.

10. Use of the composite bio-based plasticizer according to claim 1 in the preparation of PVC products.

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