A method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst
By using sodium bisulfate as a catalyst in poly3-hydroxybutyrate and recycling the catalyst through distillation and crystallization technology, the problem of difficulty in recycling concentrated sulfuric acid catalysts and environmental pollution is solved, and high-efficiency and low-cost R Preparation of -3-hydroxybutyrate, high catalyst recovery and high yield.
Patent Information
- Application Number
- CN202211270680.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-10-14
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2042-10-14
AI Technical Summary
In the prior art, when concentrated sulfuric acid catalyzes as a catalyst for the degradation of poly3-hydroxybutyrate, R-3-hydroxybutyrate, the catalyst is difficult to recover, has high environmental pollution, hassle of post-treatment and high cost.
Sodium bisulfate is used as a catalyst to react with poly3-hydroxybutyrate in an alcohol solution, and the catalyst is separated and reused by distillation and crystallization, reducing the cost of the catalyst and environmental pollution.
It realizes the operation of the catalytic process, green and environmentally friendly, efficient recycling and reuse of catalysts, and reduces production costs. The yield of the product R-3-hydroxybutyrate reaches 128 wt%, and the catalyst recovery rate reaches 96%, solving the traditional solution. The environmental pollution and inability to recover the acid catalyst.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of poly 3-hydroxybutyrate utilization, and relates to a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate by using sodium bisulfate as a catalyst. Background Art
[0002] R-3-hydroxybutyrate compounds (such as R-3-hydroxybutyrate methyl ester and R-3-hydroxybutyrate ethyl ester) are an important class of chiral compounds. Among them, R-3-hydroxybutyrate methyl ester is believed to have a certain therapeutic effect on neurodegenerative diseases (such as Alzheimer's disease): R-3-hydroxybutyrate methyl ester can significantly increase the metabolic activity of glial cells and improve the learning and memory ability of normal mice and Alzheimer's model mice. In addition, R-3-hydroxybutyrate methyl ester can also be used as an oxygen-containing liquid fuel (such as with 97 # It can be mixed with gasoline, with the added content reaching 5~20% v / v), thus providing a potential liquid fuel option for the global petrochemical energy crisis.
[0003] R-3-hydroxybutyrate can be obtained by heating poly-3-hydroxybutyrate in an alcohol solution system with an acid or base as a catalyst. Alkaline catalysts easily lead to the formation of a large number of by-products such as methyl crotonate, which is not suitable for industrial use. In contrast, acid catalysts have obvious advantages in terms of R-3-hydroxybutyrate product selectivity. In the process of preparing R-3-hydroxybutyrate by acid-catalyzed alcoholysis of poly-3-hydroxybutyrate, sulfuric acid is the most commonly used strong acid catalyst. However, sulfuric acid is highly corrosive, which brings inconvenience to the reaction operation; and sulfuric acid is difficult to separate and recycle for reuse after the reaction, and a large amount of alkali is required for neutralization treatment, which not only brings environmental problems, but also causes additional costs. For example, Lee et al. published a method for chemically depolymerizing poly-(R)-(-)-3-hydroxybutyrate to optically active R-(-)-3-hydroxybutyrate, first recovering poly-(R)-(-)-3-hydroxybutyrate from bacterial cells, and then performing acid alcoholysis. The alcoholysis method is as follows: the purified PHB is dissolved in 1,2-dichloroethane, an alcohol (methanol, ethanol or propanol) and a solution of hydrochloric acid, refluxed and boiled, cooled to room temperature after the reaction is completed, washed with a semi-saturated sodium chloride aqueous solution, a saturated sodium bicarbonate aqueous solution and a saturated sodium chloride aqueous solution in sequence, the three water layers are combined and extracted twice with dichloromethane, and the combined extract is added to the organic layer and dried over magnesium sulfate, and R-(-)-3-hydroxybutyrate is obtained by rotary evaporation and vacuum distillation. Although the document uses concentrated hydrochloric acid as a catalyst to prepare the corresponding 3-hydroxybutyrate, hydrochloric acid is highly corrosive, has high requirements on equipment, is not easy to operate, and is difficult to recycle the catalyst. In addition, neutralization and water washing are required during post-treatment, which will result in a large amount of wastewater, severe environmental pollution and high costs (Lee et al. Preparation of alkyl (R)-(-)-3-hydroxybutyrate by acidic alcoholysis of poly-(R)-(-)-3-hydroxybutyrate. [J]. Enzyme and microbial technology, 2000, 27(1-2): 33-36.).
[0004] Therefore, it is of great significance to develop green, environmentally friendly, easy-to-operate and recyclable acid catalysts to convert poly 3-hydroxybutyrate into R-3-hydroxybutyrate compounds. Summary of the invention
[0005] In view of the technical problems in the prior art that concentrated sulfuric acid is used as a catalyst to catalyze the degradation of poly 3-hydroxybutyrate to prepare R-3-hydroxybutyrate, the catalyst is difficult to recycle, the environmental pollution is large, the post-treatment is troublesome, and the cost is high, the present invention proposes a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst. The conversion of poly 3-hydroxybutyrate into R-3-hydroxybutyrate compounds not only meets the requirements of convenient catalytic process operation and green environmental protection, but also realizes the separation, recovery and reuse of the catalyst and reduces the catalyst cost, and has industrial application value.
[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:
[0007] A method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, comprising: adding poly 3-hydroxybutyrate, sodium bisulfate catalyst, and a mixed solution of alcohol (methanol or ethanol) and chloroform (or dichloroethane) into a reactor, reacting at 80-120° C. for 3-24 hours, and cooling to obtain a reaction solution; adding water into the reaction solution, stirring, and then pouring the solution into a separatory funnel to separate the layers, wherein the upper layer is a chloroform or dichloroethane phase (containing almost all R-3-hydroxybutyrate compounds and part of methanol), and the lower layer is a saturated or nearly saturated sodium bisulfate aqueous solution (containing part of methanol).
[0008] Based on the difference in boiling points between the solvent (chloroform (or dichloroethane) and methanol mixed solution) and the target product (R-3-hydroxybutyrate ester compounds), the product separation was achieved by two-step distillation: first, atmospheric distillation was performed between 60 and 95 °C to recover chloroform and dichloroethane, and then reduced pressure distillation was performed between 45 and 100 °C (1×10 5 ~1×10 3 Pa) distillation to recover the target product.
[0009] The obtained sodium bisulfate aqueous solution is evaporated and concentrated at 100°C, and then cooled to about 5-10°C to crystallize to obtain sodium bisulfate, which is collected and reused.
[0010] The catalyst sodium bisulfate used in the present invention can not only play a good acid catalytic effect in the alcoholysis process of poly 3-hydroxybutyrate, but also can be recycled and reused. The possible principle is: sodium bisulfate can be ionized into sulfuric acid and sodium sulfate in an alcohol solvent, and the generated sulfuric acid will play a good catalytic effect in the reaction system, thereby realizing the acid-catalyzed degradation of poly 3-hydroxybutyrate; when water is added to the reaction solution after the reaction is completed, the sulfuric acid and sodium sulfate in the reaction system will be dissolved in the water, and sodium bisulfate is obtained by evaporating and concentrating the water and cooling and crystallizing, thereby realizing the recovery and reuse of sodium bisulfate.
[0011] The present invention has the following beneficial effects:
[0012] The present invention provides a method for catalyzing the degradation of poly 3-hydroxybutyrate to R-3-hydroxybutyrate using sodium bisulfate as a catalyst. The process is simple, easy to operate, low in cost, and realizes the recovery and reuse of the catalyst, which solves the pain points of traditional homogeneous acid catalysts, such as large environmental pollution, inability to recycle and reuse, and troublesome post-processing, and has broad application prospects. In addition, when the preparation method provided by the present invention is calculated based on the mass of the raw material poly 3-hydroxybutyrate for product yield calculation, the yield of R-3-hydroxybutyric acid methyl ester prepared can reach up to 128wt%; the sodium bisulfate catalyst recovery rate reaches 96%, and the product yield and catalyst recovery rate are high. BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0014] Figure 1 This is a flow chart of the operation process of Example 1 of the present invention.
[0015] Figure 2 This is a diagram showing the separation of the chloroform phase and the sodium bisulfate aqueous solution in Example 1 of the present invention.
[0016] Figure 3 This is a GC-MS analysis chart of the R-3-hydroxybutyrate product prepared in Example 1 of the present invention.
[0017] Figure 4 This is a gas chromatography-hydrogen ion flame detector (GC-FID) analysis chart of the R-3-hydroxybutyrate product prepared in Example 1 of the present invention. DETAILED DESCRIPTION
[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0019] Example 1
[0020] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst (the entire process is shown in Figure 1 ), the steps are as follows:
[0021] (1) Take 20 g of poly (3-hydroxybutyrate), 20 g of sodium bisulfate, and 150 mL of chloroform-methanol solution (the volume ratio of chloroform to methanol is 2:1) and add them to a 300 mL reactor. Close the reactor, turn on mechanical stirring (100 rpm), raise the temperature to 90 °C and react at this temperature for 6.5 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanical stirring is performed for 30 min to obtain a two-phase solution.
[0022] (2) The two-phase solution obtained in step (1) was allowed to stand in a separatory funnel to separate the layers (see Figure 2 ), and collect the upper chloroform phase solution and the lower sodium bisulfate solution respectively. The chloroform phase solution was qualitatively analyzed by gas chromatography-mass spectrometry (see Figure 3 ) and gas chromatography-hydrogen ion flame detector quantitative analysis (see Figure 4 ), it was determined that the chloroform phase contained R-3-hydroxybutyric acid methyl ester, and its yield reached 128wt% (based on the mass of poly 3-hydroxybutyrate).
[0023] (3) distilling the chloroform phase solution obtained in step (2) at 60-80°C under normal pressure. Specifically, distilling at 60°C to prevent the solvent from spraying out, and slowly heating to 80°C for distillation after most of the solvent has been evaporated. After the solvent is completely evaporated, the reaction solvent (chloroform and methanol) is recovered. Then, the remaining liquid is slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 90 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid methyl ester.
[0024] (4) The sodium bisulfate solution obtained in step (2) was evaporated and concentrated at 100° C., then crystallized at 5° C., and finally dried at 100° C. to obtain 19.2 g of sodium bisulfate crystals, with a catalyst recovery rate of 96%. The sodium bisulfate crystals can be repeatedly used in the catalytic degradation reaction of poly 3-hydroxybutyrate.
[0025] Example 2
[0026] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, and the steps are as follows:
[0027] (1) Take 20 g of poly (3-hydroxybutyrate), 20 g of sodium bisulfate, and 150 mL of chloroform-methanol solution (the volume ratio of chloroform to methanol is 1:1) and add them to a 300 mL reactor. Close the reactor, turn on the mechanical stirring (100 rpm), raise the temperature to 100 °C and react at this temperature for 5 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanically stir for 30 min to obtain a two-phase solution.
[0028] (2) The two-phase solution obtained in step (1) was allowed to stand in a separatory funnel to separate the layers, and the upper chloroform phase solution and the lower sodium bisulfate solution were collected respectively. The chloroform phase solution was subjected to qualitative analysis by gas chromatography-mass spectrometry and quantitative analysis by gas chromatography-hydrogen ion flame detector to determine that the chloroform phase contained R-3-hydroxybutyric acid methyl ester, and its yield reached 116wt% (based on the mass of poly 3-hydroxybutyrate).
[0029] (3) distilling the chloroform phase solution obtained in step (2) at 60-80°C under normal pressure. Specifically, distilling at 60°C to prevent the solvent from spraying out, and slowly heating to 80°C for distillation after most of the solvent has been evaporated. After the solvent is completely evaporated, the reaction solvent (chloroform and methanol) is recovered. Then, the remaining liquid is slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 90 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid methyl ester.
[0030] (4) The sodium bisulfate solution obtained in step (2) is evaporated and concentrated at 100° C., then crystallized at 5° C., and finally dried at 100° C. to obtain 19.1 g of sodium bisulfate. The recovered sodium bisulfate can be reused in the catalytic degradation reaction of poly (3-hydroxybutyrate).
[0031] Example 3
[0032] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, and the steps are as follows:
[0033] (1) Take 20 g of poly (3-hydroxybutyrate), 10 g of sodium bisulfate, and 150 mL of chloroform-methanol solution (the volume ratio of chloroform to methanol is 2:1) and add them to a 300 mL reactor. Close the reactor, turn on mechanical stirring (100 rpm), raise the temperature to 120 °C and react at this temperature for 3 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanical stirring is performed for 30 min to obtain a two-phase solution.
[0034] (2) The two-phase solution obtained in step (1) is allowed to stand in a separatory funnel to separate the layers, and the upper chloroform phase solution and the lower sodium bisulfate solution are collected separately. The chloroform phase solution is subjected to qualitative analysis by gas chromatography-mass spectrometry and quantitative analysis by gas chromatography-hydrogen ion flame detector to determine that the chloroform phase contains R-3-hydroxybutyric acid methyl ester, and its yield is 91wt% (based on the mass of poly 3-hydroxybutyrate).
[0035] (3) distilling the chloroform phase solution obtained in step (2) at 60-80°C under normal pressure. Specifically, distilling at 60°C to prevent the solvent from spraying out, and slowly heating to 80°C for distillation after most of the solvent has been evaporated. After the solvent is completely evaporated, the reaction solvent (chloroform and methanol) is recovered. Then, the remaining liquid is slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 90 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid methyl ester.
[0036] (4) The sodium bisulfate solution obtained in step (2) is evaporated and concentrated at 100° C., then crystallized at 5° C., and finally dried at 100° C. to obtain 9.1 g of sodium bisulfate. The recovered sodium bisulfate can be reused in the catalytic degradation reaction of poly (3-hydroxybutyrate).
[0037] Example 4
[0038] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, and the steps are as follows:
[0039] (1) Take 20 g of poly (3-hydroxybutyrate), 20 g of sodium bisulfate, and 150 mL of chloroform-ethanol solution (the volume ratio of chloroform to ethanol is 2:1) and add them to a 300 mL reactor. Close the reactor, turn on the mechanical stirring (100 rpm), raise the temperature to 100 °C and react at this temperature for 6 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanically stir for 30 min to obtain a two-phase solution.
[0040] (2) The two-phase solution obtained in step (1) was allowed to stand in a separatory funnel to separate the layers, and the upper chloroform phase solution and the lower sodium bisulfate solution were collected respectively. The chloroform phase solution was subjected to qualitative analysis by gas chromatography-mass spectrometry and quantitative analysis by gas chromatography-hydrogen ion flame detector to determine that the chloroform phase contained R-3-hydroxybutyric acid ethyl ester, and its yield reached 126wt% (based on the mass of poly 3-hydroxybutyrate).
[0041] (3) The chloroform phase solution obtained in step (2) is distilled at 60-90°C under normal pressure. Specifically, it is first distilled at 60°C to prevent the solvent from spraying out. After most of the solvent is evaporated, the temperature is slowly raised to 90°C for distillation. After the solvent is completely evaporated, the reaction solvent (chloroform and ethanol) is recovered. Then, the remaining liquid is first slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 100 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid ethyl ester.
[0042] (4) The sodium bisulfate solution obtained in step (2) is evaporated and concentrated at 100° C., then crystallized at 5° C., and finally dried at 100° C. to obtain 19.2 g of sodium bisulfate. The recovered sodium bisulfate can be reused in the catalytic degradation reaction of poly 3-hydroxybutyrate.
[0043] Example 5
[0044] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, and the steps are as follows:
[0045] (1) Take 20 g of poly (3-hydroxybutyrate), 20 g of sodium bisulfate, and 150 mL of dichloroethane-methanol solution (the volume ratio of dichloroethane to methanol is 2:1) and add them to a 300 mL reactor. Close the reactor, turn on mechanical stirring (100 rpm), raise the temperature to 80 °C and react at this temperature for 24 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanical stirring is performed for 30 min to obtain a two-phase solution.
[0046] (2) The two-phase solution obtained in step (1) was allowed to stand in a separatory funnel to separate the layers, and the upper dichloroethane phase solution and the lower sodium bisulfate solution were collected separately. The dichloroethane phase solution was subjected to qualitative analysis by gas chromatography-mass spectrometry and quantitative analysis by gas chromatography-hydrogen ion flame detector to determine that the dichloroethane phase contained R-3-hydroxybutyric acid methyl ester, and its yield reached 112wt% (based on the mass of poly 3-hydroxybutyrate).
[0047] (3) The dichloroethane phase solution obtained in step (2) is distilled at 80-95°C under normal pressure. Specifically, it is first distilled at 80°C to prevent the solvent from spraying out. After most of the solvent is evaporated, the temperature is slowly raised to 95°C for distillation. After the solvent is completely evaporated, the reaction solvent (dichloroethane and methanol) is recovered. Then, the remaining liquid is first slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 100 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid methyl ester.
[0048] (4) The sodium bisulfate solution obtained in step (2) is evaporated and concentrated at 100° C., then crystallized at 5° C., and finally dried at 100° C. to obtain 19.1 g of sodium bisulfate. The recovered sodium bisulfate can be reused in the catalytic degradation reaction of poly (3-hydroxybutyrate).
[0049] Example 6
[0050] This embodiment is a method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, and the steps are as follows:
[0051] (1) Take 20 g of poly (3-hydroxybutyrate), 15 g of sodium bisulfate, and 150 mL of dichloroethane ethanol solution (the volume ratio of dichloroethane to ethanol is 2:1) and add them to a 300 mL reactor. Close the reactor, turn on the mechanical stirring (100 rpm), raise the temperature to 90 °C and react at this temperature for 12 h, then cool to room temperature and add 75 mL of water to the reactor. Mechanically stir for 30 min to obtain a two-phase solution.
[0052] (2) The two-phase solution obtained in step (1) is allowed to stand in a separatory funnel to separate the layers, and the upper dichloroethane phase solution and the lower sodium bisulfate solution are collected separately. The dichloroethane phase solution is subjected to qualitative analysis by gas chromatography-mass spectrometry and quantitative analysis by gas chromatography-hydrogen ion flame detector to determine that the dichloroethane phase contains R-3-hydroxybutyric acid ethyl ester, and its yield is 109wt% (based on the mass of poly 3-hydroxybutyrate).
[0053] (3) The dichloroethane phase solution obtained in step (2) is distilled at 80-95°C under normal pressure. Specifically, the distillation is first performed at 80°C to prevent the solvent from spraying out. After most of the solvent has been evaporated, the temperature is slowly raised to 95°C for distillation. After the solvent is completely evaporated, the reaction solvent (dichloroethane and ethanol) is recovered. Then, the remaining liquid is first slowly distilled at 45°C under reduced pressure (1×10 5 ~1×10 3 Pa), and slowly raise the temperature to 100 °C to continue vacuum distillation to finally obtain R-3-hydroxybutyric acid ethyl ester.
[0054] (4) The sodium bisulfate solution obtained in step (2) is evaporated and concentrated at 100° C., then crystallized at 10° C., and finally dried at 100° C. to obtain 13.4 g of sodium bisulfate. The recovered sodium bisulfate can be reused in the catalytic degradation reaction of poly (3-hydroxybutyrate).
[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst, characterized in that: The poly 3-hydroxybutyrate, sodium bisulfate catalyst and mixed solvent are uniformly mixed and reacted, after the reaction is completed, the temperature is lowered, water is added, stirred and separated, the upper layer solution is distilled to recover the solvent and the target product, and the lower layer solution is evaporated and concentrated, cooled and crystallized to recover the sodium bisulfate; The mixed solvent is a mixture of an alcohol solvent and dichloroethane or chloroform, and the alcohol solvent is methanol or ethanol; The reaction temperature is 80-120°C; The reaction time is 3 to 24 hours; The upper layer solution is a solvent phase, and the solvent phase contains the target product R-3-hydroxybutyrate; the lower layer solution is a saturated or nearly saturated sodium bisulfate aqueous solution phase; The distillation is a two-step distillation method, firstly, the solvent is recovered by atmospheric distillation at 60-95° C., and then the R-3-hydroxybutyrate is recovered by reduced pressure distillation at 45-100° C.
2. The method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst according to claim 1, characterized in that: The mass ratio of the poly 3-hydroxybutyrate to sodium bisulfate is 20:(10~20).
3. The method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst according to claim 2, characterized in that: The volume ratio of the alcohol solvent to dichloroethane or chloroform is 1:(1-2).
4. The method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst according to claim 3, characterized in that: The temperature of the evaporation concentration is 100°C.
5. The method for preparing R-3-hydroxybutyrate by catalyzing the degradation of poly 3-hydroxybutyrate using sodium bisulfate as a catalyst according to any one of claims 1 to 4, characterized in that: The temperature of the cooling crystallization is 5-10°C.