Recovery method of biodegradable polyester
A hydrolysis and repolymerization process using ferric chloride and strong acids in water recycles biodegradable polyesters efficiently and cost-effectively, addressing the limitations of existing methods by maintaining mechanical properties and reducing environmental impact.
Patent Information
- Application Number
- CN202310670070.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-07
- Publication Date
- 2024-12-10
AI Technical Summary
Existing recycling methods for biodegradable polyesters, such as PBS, are costly, environmentally unfriendly, and inefficient, with high catalyst costs and complex separation processes, limiting their application and mechanical properties.
A hydrolysis process using ferric chloride and/or strong acids as catalysts in water as a solvent, followed by esterification and polycondensation, recycles biodegradable polyesters into small molecules like dibasic acid and diol, which are then repolymerized to maintain mechanical properties.
The method achieves high recovery rates and yields of biodegradable polyester monomers, enabling closed-loop recycling suitable for industrial production with minimal environmental impact and preserving mechanical properties.
Smart Images
Figure CN119100908A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of recycling technology, and more specifically, to a method for recycling biodegradable polyester. Background Art
[0002] Plastic is one of the most used materials in modern society, and it has profoundly changed human life. However, in recent decades, with the extensive use of plastic products, plastic waste in the environment has continued to accumulate, and a large amount of discarded plastic has leaked into nature, posing a serious threat to the terrestrial and marine ecological environment.
[0003] Biodegradable polyester refers to a material that is degraded under specific conditions (anaerobic digestion conditions, composting conditions, etc.) or the action of water and microorganisms in nature, and can be completely degraded and returned to nature under the action of microorganisms. For example, polybutylene succinate (PBS) is a polyester obtained by copolymerization of 1,4-succinic acid and 1,4-butanediol. It not only has excellent mechanical properties, heat resistance and good processing properties, but also has good biodegradability in compost and soil. It is an important biodegradable polyester plastic and a highly-regarded "plastic ban" alternative product. It has important applications in plastic packaging, agricultural films, biomedicine and other fields. For example, after use, PBS products can be degraded by microorganisms in nature to form CO2 end products, thereby eliminating the generation of white pollution at the source. However, biodegradation also means the waste of carbon resources and the generation of greenhouse effects. In contrast, recycling and reusing biodegradable polyester as much as possible is more in line with the concept of sustainable development and the principle of circular economy, and is also of great significance to the realization of the "dual carbon" goals proposed by the country.
[0004] The recycling process of biodegradable polyester can be divided into two types: physical recycling and chemical recycling. Physical recycling is to crush, clean, screen and granulate waste polyester plastics. However, in the physical recycling process, the separation of different plastics is relatively complicated and impurities are not easy to remove. Therefore, it is only suitable for recycling plastics with a relatively low degree of pollution. In addition, the mechanical properties of plastics will decrease significantly during the secondary thermoforming process, which imposes certain restrictions on its application. Chemical recycling is to depolymerize waste polyester plastics into small molecules through hydrolysis, alcoholysis, etc., and reuse them as raw materials after separation and purification. In comparison, chemical recycling has a wider range of applications and generally does not affect the performance of subsequent materials.
[0005] Regarding the recycling of biodegradable polyesters, for example, regarding the chemical recycling of PBS, patent CN113173856A reports a method for recycling PBS by alcoholysis using a zinc catalyst, but the catalyst cost is high and an organic solvent is required, which is not environmentally friendly. Therefore, it is of great significance to develop a new system that is economical, efficient and environmentally friendly to realize the recycling cycle of biodegradable polymers-raw materials-biodegradable polymers, which is more in line with the concept of sustainable development. Summary of the invention
[0006] Based on this, the object of the present invention is to provide a method for recycling biodegradable polyester, which is simple, environmentally friendly and low-cost, and has a high recovery rate.
[0007] In order to achieve the above object, the present invention adopts the following technical solutions:
[0008] A method for recycling biodegradable polyester comprises the following steps:
[0009] In the presence of a catalyst, the biodegradable polyester is subjected to a hydrolysis reaction;
[0010] Wherein, the catalyst is selected from ferric chloride and / or strong acid.
[0011] In the present technical solution, the hydrolysis process of the biodegradable polyester is the process of generating the corresponding small molecule monomer carboxylic acid and monomer alcohol. Specifically, the products obtained after the hydrolysis reaction of the biodegradable polyester include dibasic acid, diol and / or diol derivatives (such as tetrahydrofuran, etc.).
[0012] In the technical solution, the catalyst is cheap and easily available, and the conversion rate of the biodegradable polyester hydrolysis reaction catalyzed by the catalyst is high, and the yield of the dibasic acid and diol obtained by the hydrolysis reaction is high.
[0013] Furthermore, the strong acid is selected from hydrochloric acid and / or sulfuric acid.
[0014] Further, the amount of the catalyst is 0-10wt% of the biodegradable polyester by mass percentage. Exemplarily, the amount of the catalyst includes, but is not limited to, 2.5-7.5wt%, 2.5-5wt%, 5-7.5wt%, 5-7wt%, 2.5wt%, 5wt%, 7.5wt% and the like of the biodegradable polyester by mass percentage. At this time, the conversion rate of the hydrolysis reaction and the yields of the dibasic acid and diol obtained by the hydrolysis reaction are high. When the amount of the catalyst is higher than 7.5wt% of the biodegradable polyester and less than or equal to 10wt% of the biodegradable polyester, the yield of the diol obtained by the hydrolysis reaction is relatively low, but the yield of tetrahydrofuran, a derivative of the diol, is high.
[0015] Furthermore, the biodegradable polyester is selected from one or more of PBS, PBAT and PBST. In the present technical solution, the biodegradable polyester can be a corresponding waste polyester material. It has been found through research that in the present technical solution, the catalyst has a good catalytic effect on the aforementioned biodegradable polyester, reflecting good selectivity for the product (dibasic acid and diol).
[0016] Furthermore, the solvent used in the hydrolysis reaction is water. In this method, the hydrolysis reaction can be carried out in pure water using water as solvent. This method is simple and environmentally friendly and pollution-free, and can reduce the cost in the production process.
[0017] Further, the amount of the solvent is 100-2000wt% of the biodegradable polyester by weight percentage. Exemplarily, the amount of the solvent is 500-2000wt%, 500-1500wt%, 500-1000wt%, 1000-1500wt%, 500wt%, 1000wt%, 1500wt%, 2000wt% of the biodegradable polyester by weight percentage. At this time, the conversion rate of the biodegradable polyester hydrolysis reaction is high, and the yields of dibasic acid and diol are both high.
[0018] Further, the temperature of the hydrolysis reaction is 25-200° C., and the time is 20-600 min. Exemplarily, the time of the hydrolysis reaction is 120-160 min, 120-300 min, 120-180 min, 120 min, 180 min, and 300 min, etc. At this time, the conversion rate of the biodegradable polyester hydrolysis reaction is high, and the yields of carboxylic acid and alcohol are both high.
[0019] Exemplarily, the temperature of the hydrolysis reaction includes, but is not limited to, 150-180°C, 150-170°C, 160-180°C, 160-170°C, 170-200°C, 150°C, 160°C, 170°C and 180°C. At this time, the conversion rate of the biodegradable polyester hydrolysis reaction is high, and the yields of dibasic and diols are high. When the reaction temperature is higher than 170°C and less than or equal to 200°C, the yield of tetrahydrofuran, a derivative of diol, is high.
[0020] Furthermore, the hydrolysis reaction is carried out under closed conditions, for example, in a closed reactor.
[0021] Furthermore, the method further comprises the step of repolymerizing the product obtained from the hydrolysis reaction to obtain the biodegradable polyester;
[0022] The repolymerization includes an esterification reaction and a polycondensation reaction performed sequentially.
[0023] Furthermore, after removing the solvent and catalyst in the system obtained after the hydrolysis reaction, an appropriate amount of raw materials may be added to carry out repolymerization.
[0024] Further, the repolymerization comprises the following steps:
[0025] esterifying the dibasic acid and / or diol obtained by the hydrolysis reaction with the diol and / or dibasic acid added to form the biodegradable polyester; and
[0026] The product obtained by the esterification reaction is subjected to a polycondensation reaction to obtain a biodegradable polyester.
[0027] Furthermore, the conditions of the polycondensation reaction include: first adjusting the vacuum degree to 1 KPa, and then reducing it to below 100 Pa.
[0028] Furthermore, the repolymerization is carried out in a glass bottle or a reaction kettle.
[0029] Through the repolymerization reaction, closed-loop recycling of biodegradable polyester was achieved.
[0030] The beneficial effects of the present invention are as follows:
[0031] In the recovery method provided by the present invention, closed-loop recovery of biodegradable polyester-raw material-biodegradable polyester is realized, and the method is simple, avoiding complicated product separation process, and is suitable for industrial production. The discarded biodegradable polyester is well utilized, and the conversion rate of the discarded biodegradable polyester is high in the whole process, and the yield of the hydrolysis product monomer dibasic acid and monomer diol is high, and the hydrolysis product also contains tetrahydrofuran, a derivative of diol, etc. At the same time, the monomer produced by the hydrolysis product can be further used as a raw material for the generation of new biodegradable polyester. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.
[0033] Figure 1 It shows that FeCl3 catalyzes the hydrolysis of PBS in the embodiment of the present invention, and the liquid phase product 1 H NMR and ESI-MS spectra.
[0034] Figure 2 The results show that the polymerization of PBS with different acid substitution ratios in the embodiments of the present invention 1 H NMR spectrum.
[0035] Figure 3 The stress-strain curves of repolymerized PBS with different acid substitution ratios in the embodiments of the present invention are shown.
[0036] Figure 4The DSC curves of the repolymerized PBS with different acid substitution ratios in the embodiments of the present invention are shown, (a) heating, (b) cooling. DETAILED DESCRIPTION
[0037] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.
[0038] Example 1
[0039] PBS hydrolysis catalyzed by different catalysts:
[0040] Specific experimental steps: 1g PBS powder (20 mesh) was placed in a hydrothermal kettle, and then a certain amount of different catalysts (wherein the molar percentage of the catalyst relative to the PBS repeating unit is shown in Table 1 below) and 10g of solvent deionized water were added respectively, and the hydrothermal kettle was screwed and closed and placed in a box furnace, heated to 170°C for 120 minutes. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the conversion rate was calculated. The results are shown in Table 1.
[0041] The conversion rate is calculated by the following formula:
[0042]
[0043] Where w0 is the original mass of the sample, and w is the mass of the sample after the reaction.
[0044] Table 1. Effect of different catalysts on PBS hydrolysis
[0045]
[0046]
[0047] As can be seen from the table above, ferric chloride and strong acids such as hydrochloric acid and sulfuric acid have a high catalytic conversion rate for this reaction. In addition, although aluminum chloride also has a good catalytic effect, its price is high.
[0048] Example 2
[0049] FeCl3 catalyzes the hydrolysis of PBS:
[0050] The hydrolysis process is as follows:
[0051]
[0052] Specific experimental steps: put 1.00g PBS powder (20 mesh) into a hydrothermal kettle, then add a certain amount of catalyst FeCl3 and solvent deionized water (the amount of catalyst and solvent relative to PBS is shown in Table 2 below), tighten the hydrothermal kettle and put it into a box furnace, heat it to a certain temperature and react for a certain time (the reaction temperature and reaction time are shown in Table 2 below). After the reaction is completed, take out the reactor and cool it to room temperature, calculate the conversion rate and product yield, and the results are shown in Table 2. Liquid product 1 H NMR and ESI-MS spectra are shown in Figure 1 As shown, the reaction conditions are: temperature 170° C., amount of catalyst relative to PBS is 5 wt %, amount of solvent is 1000 wt %, and reaction time is 180 min.
[0053] Table 2. PBS conversion rate and product yield under different reaction conditions
[0054]
[0055]
[0056] The yield of the above products was obtained by titration and calculation of the proton peak area of H-NMR spectrum.
[0057] Example 3
[0058] Repolymerization of PBS hydrolyzate:
[0059] Specific experimental steps: 50.00g PBS particles were placed in a 1.5L reactor, and then 500mL deionized water and 2.5g FeCl3 were added. The reactor was tightened and closed, and the temperature was raised to 170℃ for 2h. After the reaction, the reactor was naturally cooled to room temperature and then opened. The system after the reaction was filtered with a 0.45μm water filter membrane to remove the Fe(OH)3 solid produced by hydrolysis. The filtrate was evaporated to remove the solvent, and then the catalyst was washed to obtain 27.51g of hydrolyzed succinic acid and 20.67g of 1,4-butanediol.
[0060] The product after the above reaction and separation is used as a raw material, and different proportions of commercially available 1,4-butanediol and succinic acid are added to carry out a polymerization reaction. The specific process is as follows:
[0061] (1) Esterification reaction: hydrolyzed succinic acid, hydrolyzed 1,4-butanediol, commercially available succinic acid, commercially available 1,4-butanediol and 0.0236 g of catalyst tetrabutyl titanate were added into a reactor equipped with a mechanical stirring system, a temperature control system and a pressure control system according to the ratio shown in Table 3. The temperature was slowly raised to 180° C. and the esterification reaction was carried out at a stirring rate of 450 rpm for about 4 hours. When the system no longer produced distillates and the top temperature dropped below 80° C., the esterification reaction was considered to be completed.
[0062] (2) Pre-polycondensation reaction: 0.1653 g of catalyst was added, the reaction system was evacuated to below 1 KPa, the temperature was raised to 190° C., and the pre-polycondensation reaction was carried out for about 1 hour.
[0063] (3) Polycondensation reaction: 0.0472 g of catalyst was added, the system was further evacuated to less than 100 Pa, and the temperature was slowly raised to 230° C. to carry out the polycondensation reaction. The system showed an obvious rod climbing phenomenon and the viscosity no longer increased significantly. The reaction was terminated when the torque of the mechanical stirring system approached the maximum value.
[0064] (4) Discharging: Release the vacuum, maintain the temperature, and take the product out of the reactor to obtain repolymerized PBS with different acid substitution ratios.
[0065] Table 3. Repolymerization PBS raw material formula with different raw material replacement ratios
[0066]
[0067]
[0068] Example 4
[0069] Structural characterization of repolymerized PBS
[0070] The structure of the repolymerized PBS in Example 3 was characterized by hydrogen nuclear magnetic resonance spectroscopy. The sample was dissolved in deuterated chloroform, TMS was used as an internal standard, and the test was performed using an AMX-300 nuclear magnetic resonance spectrometer from Bruker, Germany. 1 H NMR spectrum Figure 2 shown.
[0071] Example 5
[0072] Characterization of mechanical properties of repolymerized PBS
[0073] The repolymerized PBS sample prepared in Example 3 was processed into a standard dumbbell-shaped specimen (25 mm × 4 mm × 2 mm) on a HAAKE MiniJet Pro injection molding machine, and then tested using a WDW-10 electronic universal material testing machine (Intron 5966, USA) at room temperature at 50 mm min -1 The specimens were stretched to fracture at a constant crosshead speed to obtain mechanical property data. To ensure the accuracy of the results, at least 5 specimens were measured for each sample and the average value was reported. The stress-strain curve of the repolymerized PBS is shown in Figure 3 The tensile strength and mechanical properties data are shown in Table 4.
[0074] Table 4 Mechanical properties of repolymerized PBS with different acid substitution ratios
[0075] Acid substitution ratio (%) Tensile strength(MPa) Elongation at break (%) 0 49.8±4.1 460.8±63.3 10 52.6±0.6 527.0±44.7 50 49.4±1.2 445.3±34.0 100 48.6±1.9 470.9±27.3
[0076] As can be seen from the table, compared with the PBS obtained by polymerization using commercially available raw materials, the mechanical properties such as tensile strength and elongation at break of the repolymerized PBS obtained by using the hydrolyzate as a raw material do not decrease significantly, indicating that using the hydrolyzate as a raw material will not have an adverse effect on the mechanical properties of the repolymerized PBS.
[0077] Example 6
[0078] Thermal properties characterization of repolymerized PBS
[0079] The thermal properties of repolymerized PBS were measured using differential scanning calorimetry in a N2 atmosphere. The gas flow rate was 50 mL / min, the temperature range was -70°C-200°C, and the heating and cooling rate was 10°C / min. The heating and cooling curves of the corresponding polymers are shown in Figure 4 As shown, its melting point (Tm), crystallization temperature (Tc), melting enthalpy (ΔHm), crystallization enthalpy (ΔHc), crystallinity (X a c ) and other parameters are shown in Table 5.
[0080] Table 5 Thermal properties of repolymerized PBS
[0081]
[0082]
[0083] As can be seen from the table, compared with the PBS obtained by polymerization using commercially available raw materials, the repolymerized PBS obtained by using the hydrolyzate as a raw material has higher crystallization temperature and crystallinity, and a slightly lower melting point, but overall, the thermal properties have not decreased significantly, indicating that using the hydrolyzate as a raw material will not have an adverse effect on the thermal properties of the repolymerized PBS.
[0084] Example 7
[0085] FeCl3 catalyzes the hydrolysis of PBAT:
[0086] The hydrolysis process is as follows:
[0087]
[0088] Specific experimental steps: 1.00g PBAT particles (20 mesh) were placed in a hydrothermal kettle, and then 0.05g FeCl3 and 10g solvent deionized water were added respectively. The hydrothermal kettle was tightened and closed and placed in a box furnace, heated to 200°C for 240 minutes. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the PBAT conversion rate and product yield were calculated. The PBAT conversion rate was 100%, the product terephthalic acid yield was 93.2%, the 1,6-hexanodioic acid yield was 95.4%, the 1,4-butanediol yield was 10.5%, and the tetrahydrofuran yield was 79.1%.
[0089] Example 8
[0090] HCl catalyzes the hydrolysis of PBAT:
[0091] The hydrolysis process is as follows:
[0092]
[0093] Specific experimental steps: 1.00g PBAT particles (20 mesh) were placed in a hydrothermal kettle, and then 0.05g 37wt% hydrochloric acid and 10g solvent deionized water were added respectively. The hydrothermal kettle was tightened and closed and placed in a box furnace, heated to 200℃ for 240min. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the PBAT conversion rate and product yield were calculated. The PBAT conversion rate was 100%, the product terephthalic acid yield was 96.4%, the 1,6-hexanodioic acid yield was 96.2%, the 1,4-butanediol yield was 6.8%, and the tetrahydrofuran yield was 82.0%.
[0094] Example 9
[0095] FeCl3 catalyzes the hydrolysis of PBST:
[0096] The hydrolysis process is as follows:
[0097]
[0098] Specific experimental steps: 1.00g PBST particles (20 mesh) were placed in a hydrothermal kettle, and then 0.05g FeCl3 and 10g solvent deionized water were added respectively. The hydrothermal kettle was tightened and closed, and then placed in a box furnace, heated to 200℃ and reacted for 240min. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the PBST conversion rate and product yield were calculated. The PBST conversion rate was 100%, the product terephthalic acid yield was 92.5%, the succinic acid yield was 96.3%, the 1,4-butanediol yield was 8.1%, and the tetrahydrofuran yield was 70.2%.
[0099] Example 10
[0100] HCl catalyzes the hydrolysis of PBST:
[0101] The hydrolysis process is as follows:
[0102]
[0103] Specific experimental steps: 1.00g PBST particles (20 mesh) were placed in a hydrothermal kettle, and then 0.05g 37wt% hydrochloric acid and 10g solvent deionized water were added respectively. The hydrothermal kettle was tightened and closed, and then placed in a box furnace, heated to 200℃ and reacted for 240min. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the PBST conversion rate and product yield were calculated. The PBST conversion rate was 100%, the product terephthalic acid yield was 96.1%, the succinic acid yield was 96.7%, the 1,4-butanediol yield was 8.6%, and the tetrahydrofuran yield was 80.7%.
[0104] Embodiment 11
[0105] Hydrochloric acid catalyzes the hydrolysis of PBS:
[0106] The hydrolysis process is as follows:
[0107]
[0108] Specific experimental steps: 1.00g PBS powder (20 mesh) was placed in a hydrothermal kettle, and then 0.05g 37wt% hydrochloric acid and 10g solvent deionized water were added respectively. The hydrothermal kettle was screwed shut and placed in a box furnace, heated to 170℃ for 180min. After the reaction was completed, the reactor was taken out and cooled to room temperature, and the PBS conversion rate and product yield were calculated. The PBS conversion rate was 100%, the product succinic acid yield was 95.8%, the 1,4-butanediol yield was 73.2%, and the tetrahydrofuran yield was 12.8%.
[0109] Example 12
[0110] Hydrochloric acid catalyzes the hydrolysis of PBS:
[0111] The hydrolysis process is as follows:
[0112]
[0113] Specific experimental steps: 1.00g PBS powder (20 mesh) was placed in a hydrothermal reactor, and then 0.05g 37wt% hydrochloric acid and 10g solvent deionized water were added respectively. The hydrothermal reactor was screwed shut and placed in a box furnace, heated to 150℃ for 300min. After the reaction was completed, the reactor was taken out and cooled to room temperature. The PBS conversion rate was 100%, the product succinic acid yield was 96.8%, the 1,4-butanediol yield was 78.2%, and the tetrahydrofuran yield was 16.3%.
[0114] Example 13
[0115] Sulfuric acid catalyzes the hydrolysis of PBS:
[0116] The hydrolysis process is as follows:
[0117]
[0118] Specific experimental steps: 1.00g PBS powder (20 mesh) was placed in a hydrothermal kettle, and then 0.05g 98wt% sulfuric acid and 10g solvent deionized water were added respectively. The hydrothermal kettle was screwed shut and placed in a box furnace, heated to 170℃ for 180min. After the reaction was completed, the reactor was taken out and cooled to room temperature. The PBS conversion rate was 100%, the product succinic acid yield was 96.3%, the 1,4-butanediol yield was 67.1%, and the tetrahydrofuran yield was 25.3%.
[0119] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.
Claims
1. A method for recycling biodegradable polyester, characterized in that: The steps include: In the presence of a catalyst, the biodegradable polyester is subjected to a hydrolysis reaction; Wherein, the catalyst is selected from ferric chloride and / or strong acid.
2. The recycling method according to claim 1, characterized in that: The biodegradable polyester is selected from one or more of PBS, PBAT and PBST.
3. The recycling method according to claim 1, characterized in that: The strong acid is selected from hydrochloric acid and / or sulfuric acid.
4. The recycling method according to claim 1, characterized in that: The solvent used in the hydrolysis reaction is water.
5. The recycling method according to any one of claims 1 to 4, characterized in that: Calculated by mass percentage, the amount of the catalyst used is 1-10wt% of the biodegradable polyester.
6. The recycling method according to any one of claims 1 to 4, characterized in that: Calculated by mass percentage, the amount of the catalyst used is 2.5-7.5wt% of the biodegradable polyester.
7. The recovery method according to any one of claims 1 to 4, characterized in that: Calculated by mass percentage, the amount of the solvent used is 100-5000wt% of the biodegradable polyester, preferably 500-5000wt%.
8. The recycling method according to any one of claims 1 to 4, characterized in that: The temperature of the hydrolysis reaction is 25-200° C., and the time is 20-600 min.
9. The recycling method according to claim 1, characterized in that: The method further comprises the step of repolymerizing the product obtained from the hydrolysis reaction to obtain the biodegradable polyester; The repolymerization includes an esterification reaction and a polycondensation reaction performed sequentially.
10. The recycling method according to claim 9, characterized in that: The repolymerization comprises the following steps: esterifying the dibasic acid and / or diol obtained by the hydrolysis reaction with the diol and / or dibasic acid added to form the biodegradable polyester; and The product obtained by the esterification reaction is subjected to a polycondensation reaction to obtain a biodegradable polyester.