A method for degrading polyalkanoates

Abstract

The application provides a polyol ester plastic degradation method, comprising the following steps: (1) mixing polyol ester plastic with alcoholysis reagent to obtain a mixed solution; wherein the mass-volume ratio of polyol ester plastic and alcoholysis reagent is (10-120):1 mg / ml; (2) adding catalyst alpha-MoC to the mixed solution, and obtaining an alkyl ester compound through a hydrogenation and deoxidation reaction under a closed protective gas atmosphere; wherein the mass ratio of catalyst and polyol ester plastic is 1:(2-20), the pressure of the protective gas is 0.1-5 MPa, the reaction temperature of the hydrogenation and deoxidation reaction is 220-240 DEG C, and the reaction time is 8-120 h. The above steps are used for degrading the polyol ester plastic, realizing a catalytic hydrogenation and deoxidation process under mild conditions, and converting the polyol ester plastic into corresponding alkyl ester compounds, thereby solving the degradation and conversion problems of the polyol ester plastic.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of organic intermediate synthesis, in particular to a degradation method of polyol ester plastic. BACKGROUND

[0002] As a new type of biodegradable plastic, polyol ester plastic is widely used in food packaging, medical and health, building materials and many other fields. Unlike petroleum-based plastics, polyol ester plastic can be degraded under the action of microorganisms to realize the recycling of carbon resources. However, the degradation rate of polyol ester plastic in nature is extremely slow, and the final degradation product is carbon dioxide. The production of carbon dioxide not only causes the greenhouse effect, but also causes the loss of carbon resources. Therefore, how to direct the conversion of polyol ester plastic into high-value chemicals on the basis of degrading polyol ester plastic has become a technical problem to be solved by those skilled in the art. SUMMARY

[0003] The application aims to provide a degradation method of polyol ester plastic to solve the degradation and conversion problems of polyol ester plastic and direct the conversion of polyol ester plastic into high-value chemicals. The specific technical scheme is as follows:

[0004] The application provides a degradation method of polyol ester plastic, which comprises the following steps:

[0005] (1) mixing the polyol ester plastic with an alcoholysis reagent to obtain a mixed solution;

[0006] The mass-volume ratio of the polyol ester plastic to the alcoholysis reagent is (10-120): 1 mg / ml.

[0007] (2) adding a catalyst alpha-MoC to the mixed solution, and carrying out a hydrogenation and deoxidation reaction under a closed protective gas atmosphere to obtain an alkyl ester compound;

[0008] The mass ratio of the catalyst to the polyol ester plastic is 1:(2-20), the pressure of the protective gas is 0.1-5 MPa, and the reaction temperature of the hydrogenation and deoxidation reaction is 160-240 DEG C, and the reaction time is 8-120 h.

[0009] The above steps are used to degrade the polyol ester plastic, realize the catalytic hydrogenation and deoxidation process under mild conditions, direct the conversion of the polyol ester plastic into the corresponding alkyl ester compound, and well solve the degradation and conversion problems of the polyol ester plastic, so that the polyol ester plastic is directly converted into high-value chemicals.

[0010] The kind of the protective gas is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the protective gas is selected from any one of nitrogen (N2), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and air, etc.

[0011] In an embodiment of the present application, before use, the catalyst is reduced in a reaction gas at 580-600°C for 1-3h; the reaction gas is selected from a mixed gas of methane and hydrogen or diluted hydrogen. The catalyst activated by the above-mentioned step is used in the degradation step of the poly-oligomeric acid ester plastic, which can exhibit excellent reactivity, so that the poly-oligomeric acid ester plastic has excellent conversion rate, the alkyl ester compound in the product after degradation and conversion has high selectivity, and the alkyl ester compound has high yield.

[0012] In an embodiment of the present application, after step (2), the catalyst α-MoC is obtained by centrifugal separation, and the catalyst α-MoC is reduced in a reaction gas at 580-600°C for 1-3h, and then is used in step (2) again. Specifically, it can be understood that after the completion of the previous degradation reaction, the catalyst α-MoC is obtained by centrifugation, and the catalyst α-MoC obtained by centrifugation is treated by the above-mentioned method, and then is recycled in the degradation reaction of the poly-oligomeric acid ester plastic. It shows that the catalyst of the present application has good cycle stability and can be recycled in the degradation of the poly-oligomeric acid ester plastic. The above-mentioned "centrifugal separation" is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0013] In an embodiment of the present application, the volume ratio of methane and hydrogen in the mixed gas is (10-20):(80-90), and the volume ratio of argon and hydrogen in the diluted hydrogen is (85-95):(5-15). The mixed gas of methane and hydrogen or the diluted hydrogen selected in the degradation of the poly-oligomeric acid ester plastic is more conducive to improving the conversion rate of the poly-oligomeric acid ester plastic and the selectivity of the alkyl ester compound.

[0014] In an embodiment of the present application, the kind of the poly-oligomeric acid ester plastic is not particularly limited, as long as the purpose of the present application can be achieved. For example, the poly-oligomeric acid ester plastic is selected from any one of polylactic acid (PLA), polyglycolic acid (PGA), and polycaprolactone (PCL). The weight average molecular weight of the poly-oligomeric acid ester plastic is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0015] The size of the poly-oligomeric acid ester plastic in the degradation process is not limited in the present application, as long as the purpose of the present application can be achieved. For example, when the mass of the poly-oligomeric acid ester plastic to be degraded is greater than 6g, the size of the poly-oligomeric acid ester plastic is cut to 2cm×2cm, so as to facilitate the reaction.

[0016] In one embodiment of this application, there is no particular limitation on the type of alkyl ester compound, as long as it can achieve the purpose of this application. For example, the alkyl ester compound is selected from any one of methyl propionate (MP), ethyl propionate, propyl propionate, methyl acetate (MA), and methyl hexanoate (MH).

[0017] In one embodiment of this application, the alcoholysis reagent is selected from any one of methanol (MeOH), ethanol (EtOH), propanol (Pol), and a mixture of methanol and p-xylene (PX); in the mixture of methanol and p-xylene, the volume ratio of methanol to p-xylene is (0.5-2):(18-19.5). Preferably, the alcoholysis reagent is EtOH, Pol, or a mixture of MeOH and PX.

[0018] In this application, conversion rate refers to the percentage of polyol ester plastics converted. Selectivity refers to the percentage of alkyl ester compounds among the various reaction products generated from the degradation of polyol ester plastics.

[0019] Beneficial effects of the embodiments in this application:

[0020] This application provides a method for degrading polyol ester plastics, comprising the following steps: (1) mixing polyol ester plastics with an alcoholysis reagent to obtain a mixed solution; wherein the mass-volume ratio of polyol ester plastics to alcoholysis reagent is (10-120):1 mg / ml; (2) adding catalyst α-MoC to the mixed solution, and obtaining alkyl ester compounds through a hydrodeoxygenation reaction under a closed protective gas atmosphere; wherein the mass ratio of catalyst to polyol ester plastics is 1:(2-20), the pressure of the protective gas is 0.1-5 MPa, the reaction temperature of the hydrodeoxygenation reaction is 220-240℃, and the reaction time is 8-120 h. By using the above steps to degrade polyol ester plastics, a catalytic hydrodeoxygenation process under mild conditions is achieved, directionally converting polyol ester plastics into corresponding alkyl ester compounds, effectively solving the degradation and conversion problems of polyol ester plastics, and enabling the directional conversion of polyol ester plastics into high-value chemicals. Polyol ester plastics exhibit excellent conversion rates, with high selectivity and yield of alkyl ester compounds among the degradation and conversion products. Furthermore, the catalyst α-MoC of this application demonstrates good cycle stability and can be recycled for the degradation of polyol ester plastics.

[0021] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0023] Figure 1 The graphs show the degradation effects of PLA in Examples 1 and 2 at different reaction temperatures.

[0024] Figure 2 The graph shows the degradation effect of PLA in Example 3 at different reaction times;

[0025] Figure 3 for Figure 2 NMR mass spectra showing the degradation effect of PLA over time;

[0026] Figure 4 The graph shows the degradation effect of PLA in Example 4 at different reaction times;

[0027] Figure 5 This is a comparison chart of the degradation effects of Examples 1, 5, and 6;

[0028] Figure 6 The graph shows the yield versus the number of cycles for the catalyst α-MoC in the catalytic system of Example 7 after 10 cycles. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0030] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0031] Test methods and equipment

[0032] Qualitative and quantitative analyses of the reaction systems of each embodiment and comparative example were performed using gas chromatography and nuclear magnetic resonance spectroscopy.

[0033] Example 1

[0034]

[0035] (1) 200 mg of polyol ester plastic PLA was mixed with 20 ml of alcoholysis reagent MeOH to obtain a mixture, wherein the weight average molecular weight of PLA was 80,000;

[0036] (2) 100 mg of catalyst α-MoC was placed in a mixture of methane and hydrogen (volume ratio of methane to hydrogen was 15:85) and reduced at 590 °C for 2 h.

[0037] (3) Add the catalyst α-MoC obtained in step (2) to the mixture obtained in step (1), and heat to a reaction temperature of 220°C under a closed N2 atmosphere with a pressure of 1 MPa for 8 h to obtain a methanol solution containing MP and Pol. The yield of MP is 93%.

[0038] Example 2

[0039] Except for adjusting the reaction temperature in step (3) to 240°C, the process was the same as in Example 1. The yield of MP was 81%.

[0040] Example 3

[0041] Except for adjusting the mass of PLA to 2g, the volume of MeOH to 50ml, and the reaction time to 96h, everything else was the same as in Example 1. The yield of MP was 95%.

[0042] Example 4

[0043] Except for replacing PLA with an actual PLA plastic product mixture (containing 2g plastic straws, 2g cups, and 2g cutlery), adjusting the total mass to 6g, the volume of MeOH to 50ml, the mass of the catalyst α-MoC to 400mg, and the reaction time to 120h, everything else was the same as in Example 1. Specifically, the PLA mass percentage in the plastic straws was 85.1%, in the cups it was 82.2%, and in the cutlery it was 73.9%, with a MP yield of 98% (based on PLA).

[0044] Example 5

[0045]

[0046] Except for replacing PLA with PGA (weight-average molecular weight 100,000), the rest is the same as in Example 1. The yield of MA is 94%.

[0047] Example 6

[0048]

[0049] Except for replacing PLA with PCL (weight-average molecular weight 80,000), the process was identical to Example 1. The yield of MH was 79%.

[0050] Example 7

[0051]

[0052] (1)-(3) are the same as in Example 1;

[0053] (4) 100 mg of catalyst α-MoC was obtained from MeOH solution by centrifugation;

[0054] (5) Same as step (1);

[0055] (6) Except for replacing 100mg of catalyst α-MoC with the 100mg of catalyst α-MoC obtained in step (4) above, the rest is the same as step (2) in Example 1;

[0056] (7) Same as step (3);

[0057] Repeat steps (4)-(7) 8 times.

[0058] Example 8

[0059] Except for replacing the alcoholysis reagent MeOH with a mixture of MeOH and PX, and setting the volume ratio of MeOH to PX to 2:18, the rest is the same as in Example 1.

[0060] Example 9

[0061] Except for the volume ratio of MeOH to PX being 1:19, everything else is the same as in Example 8.

[0062] Example 10

[0063] Except for the volume ratio of MeOH to PX being 0.5:19.5, everything else is the same as in Example 8.

[0064] Example 11

[0065] Except for replacing the alcoholysis reagent MeOH with EtOH and changing the reaction time to 22h, everything else is the same as in Example 1.

[0066] Example 12

[0067] Except for replacing the alcoholysis reagent MeOH with Pol and changing the reaction time to 40h, everything else is the same as in Example 1.

[0068] Comparative Example 1

[0069]

[0070] (1) Same as Example 1;

[0071] (2) Add catalyst β-Mo2C to the mixture obtained in step (1), heat to 220°C under a closed N2 atmosphere with a pressure of 1 MPa, and react for 8 h to obtain a methanol solution containing methyl lactate (ML) and MP.

[0072] Comparative Example 2

[0073]

[0074] Except for the use of γ-Mo2N as the catalyst, everything else is the same as in Comparative Example 1.

[0075] Comparative Example 3

[0076]

[0077] In addition to selecting α-MoC b As a catalyst, step (3) of the reaction yields a methanol solution containing ML, MP and Pol, but otherwise it is the same as in Example 1.

[0078] α-MoC b It is prepared by passivating α-MoC after activation treatment in step (2) of Example 1 under a mixed gas atmosphere of oxygen (O2) and argon (Ar) (the volume ratio of O2 to Ar is 0.5:99.5).

[0079] Comparative Example 4

[0080]

[0081] Except for the use of MoO3 as a catalyst, the reaction in step (2) yields a methanol solution containing ML, MP and Pol, which is otherwise the same as Comparative Example 1.

[0082] Comparative Example 5

[0083]

[0084] Except for the use of W2C as the catalyst, everything else is the same as in Comparative Example 1.

[0085] Comparative Example 6

[0086]

[0087] Except for the use of 3Pt / SiO2 as the catalyst, the rest is the same as Comparative Example 4.

[0088] Comparative Example 7

[0089]

[0090] Except for the use of 1Pt / γ-Al2O3 as the catalyst, everything else is the same as in Comparative Example 1.

[0091] Comparative Example 8

[0092]

[0093] Except for the use of 3Pt / TiO2 as the catalyst, everything else is the same as in Comparative Example 1.

[0094] Comparative Example 9

[0095]

[0096] Except for replacing N2 with H2, everything else is the same as Comparative Example 8.

[0097] Comparative Example 10

[0098]

[0099] Except for not using a catalyst, the reaction in step (2) yields a methanol solution containing ML, which is the same as in Comparative Example 1.

[0100] The test results of Examples 1-12 and Comparative Examples 1-10 are shown in Tables 1-3 and 1-3. Figures 1-6 As shown.

[0101] Table 1. Results of PLA depolymerization and conversion under different conditions in Example 1 and Comparative Examples 1-10.

[0102]

[0103] Note: α-MoC in Comparative Example 3 b The "b" in the text refers to the passivation treatment of α-MoC treated in step (2) of Example 1 under a mixed gas atmosphere of O2 and Ar with a volume ratio of 0.5:99.5; and the 3Pt / TiO2 of Comparative Example 9. c The "c" in Comparative Example 9 refers to replacing N2 with H2 in Comparative Example 8. Carbon balance = (Amount of lactic acid monomer in all products after reaction) / (Amount of lactic acid monomer in feed) × 100%.

[0104] Table 1 above shows the depolymerization and conversion results of PLA in Example 1 and Comparative Examples 1-10 under different conditions. Specifically, it can be understood as the depolymerization and conversion results of PLA in Example 1 and Comparative Examples 1-8, and Comparative Example 10 under different catalysts, and the depolymerization and conversion results of PLA in Comparative Example 9 and Comparative Example 8 under different protective atmospheres. As can be seen from Table 1, compared to Comparative Examples 1-8, the catalyst α-MoC in Example 1 exhibited excellent reactivity. After 8 hours of reaction, the PLA conversion rate was greater than 99%, the selectivity of the alkyl ester compound MP reached 94%, and the MP yield reached 93%. In contrast, among Comparative Examples 1-8 and Comparative Example 10, Comparative Example 6, which used the more active 3Pt / SiO2, showed a PLA conversion rate greater than 99%, an MP selectivity of 38%, and an MP yield of 39%, significantly worse than the effect of Example 1. This indicates that using the catalyst α-MoC of Example 1 effectively solved the degradation and conversion problem of polyol ester plastics, enabling the directional conversion of polyol ester plastics into high-value chemicals. As can be seen from Example 1 and Comparative Example 3, when the catalyst α-MoC is activated before use and then applied to the degradation step of polyol ester plastics, it exhibits better reactivity, resulting in higher conversion rate of polyol ester plastics, higher selectivity of alkyl ester compounds, and higher yield.

[0105] Figure 1 The degradation effects of PLA in Examples 1 and 2 at different reaction temperatures are shown in the graphs. Figure 1 As shown, in Example 1, when PLA was reacted at a reaction temperature of 220°C for 8 hours, the yield of MP reached as high as 93%; in Example 2, when PLA was reacted at a reaction temperature of 240°C for 8 hours, the yield of MP reached 81%; when PLA was reacted at the same temperatures of 160°C, 180°C, and 200°C for 8 hours, the yield of MP was less than or equal to 50%. This indicates that the reaction temperature within the range of this application effectively solves the degradation and conversion problems of polyol ester plastics. It can be observed that increasing the reaction temperature increases the amount of over-hydrogenated byproduct Pol generated during the reaction. Preferably, when the reaction temperature of 220°C in Example 1 is used, the selectivity and yield of the alkyl ester compound MP are higher.

[0106] Figure 2 The degradation effect of PLA in Example 3 at different reaction times is shown in the figure. Figure 3 for Figure 2 NMR mass spectra showing the change in PLA degradation efficiency over time. Figure 2 and Figure 3As shown, in the catalytic system of Example 3, after 12 hours of reaction, the conversion rate of PLA was greater than 99%, a large amount of ML was generated, and the yield of MP was 18%. As the reaction time increased, the ML gradually decreased and the yield of MP gradually increased. When the reaction time was 96 hours, the reaction was relatively complete, the yield of MP was about 95%, and the perhydrogenated product Pol with a yield of 5% was produced.

[0107] Figure 4 The graph shows the degradation effect of PLA in Example 4 at different reaction times, such as... Figure 4 As shown, in the catalytic system of Example 4, after 12 hours of reaction, the conversion rate of PLA was greater than 99%, and a large amount of ML was generated. As the reaction time increased, the ML gradually decreased and the yield of MP gradually increased. When the reaction time was 120 hours, the yield of MP could reach 98%.

[0108] Figure 5 The graph shows a comparison of the degradation effects of Examples 1, 5, and 6. Figure 5 As shown, in the same catalytic system, PGA and PLA exhibit similar degradation effects. PLA reacts to selectively generate alkyl ester compounds MP, with a yield of 93%. PGA reacts to selectively generate alkyl ester compounds MA, with a yield of 94%. PCL degrades to selectively generate alkyl ester compounds MH, with a yield of 79%, lower than the yields of MP and MA. PCL degradation also produces some other compounds besides MH. This may be attributed to the fact that PCL has a longer carbon chain, making it more flexible and more difficult to bind to the reaction sites on the catalyst compared to PGA and PLA, thus requiring a longer reaction time to achieve a higher yield of MH. Therefore, the catalytic hydrodeoxygenation system of this application has good universality and can convert different types of polyol ester plastics into corresponding alkyl ester compounds with high selectivity and high conversion rate, thereby realizing the catalytic process for the targeted conversion of biodegradable polyol ester plastics into high-value chemicals.

[0109] Figure 6 The diagram shows the yield-cycle number of times the catalyst α-MoC was recycled 10 times in the catalytic system of Example 7. Specifically, it can be understood that after each degradation reaction, the catalyst α-MoC was centrifuged to obtain α-MoC, which was then reactivated. The activated catalyst α-MoC was then reused in the PLA degradation reaction. Figure 6 As can be seen, the reactivity of the catalytic system did not change significantly in 10 cycles, indicating that the catalyst α-MoC has good cycle stability and can be recycled for the degradation of polyol ester plastics.

[0110] Table 2. Liquid phase product analysis of PLA under different alcoholysis reagents in Examples 1 and 8-12.

[0111]

[0112] Note: In Table 2, “b” indicates that HA is methyl lactate in Examples 1 and 8-10, ethyl lactate in Example 11, and propyl lactate in Example 12; AE is methyl propionate in Examples 1 and 8-10, ethyl propionate in Example 11, and propyl propionate in Example 12; and Aol is propanol in Examples 1 and 8-12. In Table 2, “c” indicates that PX is p-xylene. In Table 2, “d” indicates that the reaction time in Example 11 is 22 h. In Table 2, “e” indicates that the reaction time in Example 12 is 40 h.

[0113] Table 3. Gas phase product analysis of PLA under different alcoholysis reagents in Examples 1 and 8-12.

[0114]

[0115] Note: In Table 3, "alcohol solvent" is MeOH in Examples 1 and 8-10, EtOH in Example 11, and Pol in Example 12; "b" in Table 3 indicates that the ester generated from MeOH in Examples 1 and 8-10 is methyl formate, the ester generated from EtOH in Example 11 is ethyl acetate, and the ester generated from Pol in Example 12 is propyl propionate; "c" in Table 3 indicates that PX is p-xylene; "d" in Table 3 indicates that the reaction time in Example 11 is 22 h; "e" in Table 3 indicates that the reaction time in Example 12 is 40 h.

[0116] Table 2 shows the liquid-phase product analysis of PLA under different alcoholysis reagents in Examples 1 and 8-12, and Table 3 shows the gas-phase product analysis of PLA under different alcoholysis reagents in Examples 1 and 8-12. As can be seen from Tables 2 and 3, in Example 1, the polyol ester plastic PLA was efficiently converted into the corresponding alkyl ester compounds via a hydrodeoxygenation reaction under the conditions of catalyst α-MoC and alcoholysis reagent MeOH. However, during the reaction, MeOH produced a certain amount of gaseous products, such as CO2, CH4, and CO, while generating hydrogen on α-MoC. The generation of gaseous products resulted in excessive consumption of MeOH (38.5 mmol, approximately 1.6 ml). In Examples 8-10, a certain amount of MeOH was replaced with PX, and excess MeOH was added (2 ml in Example 8, 1 ml in Example 9, and 0.5 ml in Example 10). As shown in Tables 2 and 3, the reduction in the amount of MeOH did not affect the occurrence of the hydrodeoxygenation reaction, and the yield of methyl propionate remained above 93%. However, the generation of CO2, CH4, and CO in the gaseous products was significantly reduced, which means that the consumption of MeOH was also reduced. In Examples 11-12, when MeOH was replaced with EtOH and Pol, respectively, PLA could still undergo a highly efficient hydrodeoxygenation reaction to produce the corresponding ethyl propionate and propyl propionate, with yields of 85% and 86%, respectively. Compared with methanol as the alcoholysis reagent, the reaction time was slightly longer, at 22 h and 40 h, respectively. Since the higher alcohol solvents EtOH and Pol cannot break carbon-carbon bonds on the catalyst α-MoC, almost no CO2, CH4, and CO were generated in the gaseous products. While producing hydrogen, liquid products such as ethyl acetate and propyl propionate were generated, thus effectively avoiding excessive consumption of alcohol solvents. Therefore, in order to avoid excessive consumption of MeOH during the reaction, the preferred alcoholysis reagent is a mixture of EtOH, Pol, and MeOH with PX, which can effectively reduce the formation of gaseous products without affecting the product yield of the hydrodeoxygenation reaction.

[0117] In summary, the degradation method described in this application achieves a mild catalytic hydrodeoxygenation process for polyol plastics, directionally converting them into corresponding alkyl ester compounds. This effectively solves the degradation and conversion problems of polyol plastics, enabling their targeted transformation into high-value chemicals. Specifically, the polyol plastics exhibit excellent conversion rates, and the alkyl ester compounds in the degradation and conversion products show high selectivity and yield. The catalyst α-MoC used in this application exhibits good cycle stability and can be recycled for the degradation of polyol plastics.

[0118] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0119] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A method for degrading poly-alicylate plastic, comprising the following steps: (1) mixing the poly-alicylate plastic with an alcoholysis reagent to obtain a mixture; wherein the mass-volume ratio of the poly-alicylate plastic to the alcoholysis reagent is (10-120) : 1 mg / ml; (2) adding a catalyst α-MoC to the mixture, and obtaining an alkyl ester compound through a hydrogenation deoxidation reaction under a closed protective gas atmosphere; wherein the mass ratio of the catalyst to the poly-alicylate plastic is 1: (2-20), the pressure of the protective gas is 0.1-5 MPa, the reaction temperature of the hydrogenation deoxidation reaction is 220-240 ℃, and the reaction time is 8-120 h; the poly-alicylate plastic is selected from any one of polylactic acid, polyglycolic acid and polycaprolactone; and the alcoholysis reagent is selected from any one of methanol, ethanol, propanol and a mixed reagent of methanol and p-xylene. The poly-alicylate plastic is selected from any one of polylactic acid, polyglycolic acid and polycaprolactone; and the alcoholysis reagent is selected from any one of methanol, ethanol, propanol and a mixed reagent of methanol and p-xylene. The catalyst is reduced in a reaction gas at 580-600 ℃ for 1-3 h before use; the reaction gas is selected from a mixed gas of methane and hydrogen or diluted hydrogen. The volume ratio of methane to hydrogen in the mixed gas is (10-20) : (80-90), and the volume ratio of argon to hydrogen in the diluted hydrogen is (85-95) : (5-15). After step (2), the catalyst is separated by centrifugation, and then is reduced in a reaction gas at 580-600 ℃ for 1-3 h before being used again in step (2). The alkyl ester compound is selected from any one of methyl propionate, ethyl propionate, propyl propionate, methyl acetate and methyl hexanoate. In the mixed reagent of methanol and p-xylene, the volume ratio of methanol to p-xylene is (0.5-2) : (18-19.5).

2. The method of claim 1, wherein, ​ ​ 3. The method of claim 2, wherein, ​ 4. The method of claim 2, wherein, ​ 5. The method of claim 1, wherein, ​ 6. The method of claim 1, wherein, ​

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