A method for preparing carboxylic acid by hydrogenolysis of polyester plastic

Abstract

The present invention provides a method for preparing carboxylic acids by hydrogenolysis of polyester plastics. The method comprises the following steps: dissolving the polyester plastic in an ionic liquid-based solvent, adding a metal catalyst, and reacting under predetermined temperature and pressure conditions to obtain polyester depolymerization products, carboxylic acids and alkanes. The ionic liquid-metal coupled catalytic system employed in the present invention offers advantages such as simplicity, high efficiency, mild reaction conditions, and simplified separation. It can efficiently catalyze the hydrogenolysis of polyesters to produce carboxylic acids and has broad industrial application prospects.

Description

Technical Field

[0001] The invention relates to a method for preparing carboxylic acid by hydrogenolysis of polyester plastics, belonging to the field of resource utilization of waste plastics. Background Art

[0002] Polyester plastics are a general term for polymers derived from the polycondensation of polyols and polyacids, primarily including polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), and polyarylates (PAR). They are a class of engineering plastics with excellent performance and a wide range of applications. The widespread use of polyester plastics has brought great convenience to people's lives, but discarded plastics also cause serious pollution and waste. From a resource utilization perspective, polyesters contain ester groups (-COO-) that can be converted into various chemicals through hydrolysis, alcoholysis, and hydrogenolysis. Therefore, their resource utilization has attracted widespread attention and become an important means of addressing the problem of waste polyester. Currently, polyester depolymerization is mainly achieved through hydrolysis, alcoholysis, and thermal decomposition, which generally require high temperatures and produce a single product. Polyester hydrogenolysis is an effective means of resource utilization. Depending on the degree of hydrogenation, compounds such as alcohols, hydrocarbons, and organic acids can be obtained, leading to significant research attention. The key to achieving polyester hydrogenolysis lies in the catalytic system. Currently, efficient catalytic systems are relatively limited, and there is an urgent need to develop new, efficient, and green catalytic systems. Therefore, related basic research and technological development are of great significance. Summary of the Invention

[0003] One objective of the present invention is to provide an ionic liquid-metal coupled catalytic system. This ionic liquid-metal coupled catalytic system can be used to hydrogenolyze polyesters to produce carboxylic acids at temperatures ranging from room temperature to 200°C and under hydrogen pressures ranging from atmospheric pressure to 10 MPa. This catalytic system is environmentally friendly, highly efficient, easily separated, and reusable.

[0004] The catalytic system provided by the present invention consists of ionic liquid and metal catalyst.

[0005] The cation of the ionic liquid can be imidazolyl cation, pyridyl cation, quaternary ammonium salt, quaternary phosphonium salt, organic base cation, etc., and the anion is mainly a halogen anion (Cl - Br - , I - ) and halogen-containing Lewis anions, etc.;

[0006] Specifically, the structural formula of the cation of the ionic liquid is as follows Figure 1 shown.

[0007] Furthermore, the ionic liquid may be selected from any one or more of the following: [BMIm][Cl], [BMIm][Br], [BMIm][I], [BMMIm][Cl], [HMIm][Br], [OMIm][I], [Ch][Cl], [Bu4P][Br], [HDBU][I], [HTMG][Cl];

[0008] The metal catalyst is a homogeneous or heterogeneous metal catalyst having a hydrogenolysis function, specifically including but not limited to nanocatalysts with active ingredients such as noble metals such as Pd, Ru, Pt, Au, and Rh, and bimetallic, multimetallic alloys, or intermetallic compounds formed with non-noble metals such as Fe, Co, Ni, Cu, and Mn (heterogeneous metal catalysts); and compounds containing at least one noble metal element of Pd, Ru, Pt, Au, and Rh (homogeneous metal catalysts);

[0009] Specifically, the metal catalyst can be: Pd / C, Pd / TiO2, Pd / montmorillonite (MMT), Pt / C, Ru / C, Rh / C, Au / C, PdNi / C, PtFe / TiO2, RuNi / MMT, RhCo / C, AuCu / C, PdCu / TiO2, PdCl2, Pd(CH3COO)2, Pd(acac)2, Ru3(CO) 12 , Rh(acac)(CO)2, Rh2(CO)4Cl2;

[0010] In the catalytic system, the molar ratio of the ionic liquid to the active metal element in the metal catalyst may be 10000:1-100, specifically 100:1, 1000:1 or 500:1.

[0011] The application of the above catalyst system in catalyzing the hydrogenolysis of polyester plastics to prepare carboxylic acids also falls within the scope of protection of the present invention.

[0012] In the application, the polyester plastic may be PET, PPT or PBT.

[0013] Another object of the present invention is to provide a method for preparing carboxylic acid by hydrogenolysis of polyester plastics.

[0014] The method for preparing carboxylic acid by hydrogenolysis of polyester plastic provided by the present invention comprises the following steps:

[0015] The polyester plastic is dissolved in an ionic liquid-based solvent, a metal catalyst is added, and the reaction is carried out under set temperature and pressure conditions to obtain polyester depolymerization products, carboxylic acids and alkanes.

[0016] In the above method, the polyester plastic can be PET, PPT or PBT;

[0017] The ionic liquid-based solvent is a pure ionic liquid or a solvent system consisting of an ionic liquid and an organic solvent;

[0018] The organic solvent is a solvent capable of dissolving polyester plastics, and can be selected from any one or a mixture of the following: tetrahydrofuran, N,N-dimethylformamide, 1,4-dioxane, ether, acetonitrile, dichloromethane, chloroform;

[0019] The weight of the active metal element in the metal catalyst accounts for 0.1%-10% of the weight of the polyester plastic; specifically, it can be 0.1%-1% or 0.5%.

[0020] In the above method, the temperature range of the hydrogenolysis reaction is room temperature to 200°C, preferably 150°C-160°C, 150°C or 160°C; the hydrogen pressure range is normal pressure to 10 MPa, preferably 6 MPa; the reaction time is 2 to 24 h, preferably 16 h-24 h, 12 h, 16 h or 24 h.

[0021] The above method may further include the operations of separating the carboxylic acid from the reaction system and recovering the ionic liquid and the metal catalyst;

[0022] The separation steps are as follows: 1) separating the heterogeneous metal catalyst from the reaction system by filtration; then, selecting an antisolvent (such as water, acetic acid, chloroform, etc.) that is miscible with the ionic liquid and insoluble or slightly soluble in the carboxylic acid based on the solubility characteristics of the ionic liquid and the carboxylic acid, adding the antisolvent to the reaction system to precipitate the carboxylic acid product, and filtering to separate the solid carboxylic acid; then, distilling the ionic liquid solution to remove the solvent, and recovering the ionic liquid for recycling;

[0023] 2) For homogeneous metal catalyst reaction systems, a suitable antisolvent is selected to precipitate the carboxylic acid from the reaction system, leaving the catalyst in the ionic liquid solution, and the solid carboxylic acid is separated by filtration; the ionic liquid solution containing the catalyst is distilled to remove the solvent, and the ionic liquid-metal catalyst is recovered and recycled.

[0024] Furthermore, the method further comprises collecting gas phase products in the separation step.

[0025] The method for preparing carboxylic acid by hydrogenolysis of polyester plastic provided by the present invention comprises the following specific steps:

[0026] Before the reaction, polyester raw materials, ionic liquid or ionic liquid-based solvent are sequentially added to a high-pressure reactor and stirred to dissolve the raw materials; then, a metal catalyst is added; after the high-pressure reactor is sealed, the air in the reactor is evacuated, and then hydrogen is introduced to a set pressure; the reactor is moved to a heating device at a set temperature and reacted for a set time; after the reaction is completed, the reactor is allowed to stand and cool to room temperature; gaseous products are collected; and the products are separated and the ionic liquid and catalyst are recovered according to the above separation steps.

[0027] The present invention has the following beneficial effects:

[0028] The ionic liquid-metal coupled catalytic system selected in the present invention has the advantages of simplicity, high efficiency, mild reaction conditions, simple separation, etc. It can efficiently catalyze the hydrogenolysis of polyester to prepare carboxylic acid and has broad industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the cationic structural formula of the ionic liquid used in the present invention. DETAILED DESCRIPTION

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0031] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0032] The present invention provides a method for preparing carboxylic acid by hydrogenolysis of polyester, comprising the following steps: dissolving the polyester in an ionic liquid-based solvent, adding a metal catalyst, and reacting under predetermined temperature and pressure conditions to obtain carboxylic acid and alkane as polyester depolymerization products. The specific steps are as follows:

[0033] Before the reaction, raw materials, ionic liquid or ionic liquid solution are sequentially added to a high-pressure reactor in a certain proportion and stirred to dissolve the raw materials; then, a certain amount of metal catalyst is added; after the high-pressure reactor is sealed, the air in the reactor is evacuated, and then hydrogen is introduced to a set pressure; the reactor is moved to a heating device at a set temperature and reacted for a set time; after the reaction is completed, the reactor is allowed to stand and cool to room temperature; gaseous products are collected; and the products are separated and the ionic liquid and catalyst are recovered according to the above separation steps.

[0034] The method of the present invention is described below with reference to specific embodiments, but the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0037] Examples 1 to 10

[0038] Before the reaction, 0.5 g of PET and 5 mL of ionic liquid were added to a 20 mL high-pressure reactor in sequence and stirred to dissolve the raw materials; then, 50 mg of a 5 wt% Pd / C nanocatalyst was added; after the high-pressure reactor was sealed, the air in the reactor was evacuated, and then hydrogen was introduced to a set pressure of 6 MPa; the reactor was moved to a heating device at 160° C. and reacted for 24 hours; after the reaction was completed, the reactor was allowed to stand and cool to room temperature; the gas phase product was collected; then, Pd / C was separated from the reaction system by centrifugal filtration, and water was added to the filtrate to precipitate terephthalic acid, which was filtered and separated to obtain a solid acid product; the ionic liquid aqueous solution was then distilled to remove water and recycled.

[0039] Table 1 Reaction conditions and reaction results of Examples 1 to 10

[0040] Example Ionic liquids p-Dibenzoic acid separation yield (%) 1 [BMIm][Cl] 97 2 [BMIm][Br] 93 3 [BMIm][I] 94 4 [BMMIm][Cl] 98 5 [HMIm][Br] 89 6 [OMIm][I] 82 7 [Ch][Cl] 85 8 <![CDATA[[Bu4P][Br]]]> 78 9 [HDBU][I] 86 10 [HTMG][Cl] 85

[0041] Examples 11 to 14

[0042] Using the ionic liquid [BMIm][Cl] of Example 1 as the solvent and the same reaction conditions as Example 1, PET hydrogenolysis studies were conducted at different temperatures. The results are listed in Table 2.

[0043] Table 2 Reaction conditions and reaction results of Examples 11 to 14

[0044] Example Reaction temperature (℃) p-Dibenzoic acid separation yield (%) 11 120 68 12 130 85 13 150 94 14 160 97

[0045] Examples 15 to 17

[0046] The ionic liquid [BMIm][Cl] in Example 1 was used as the solvent and the other reaction conditions were the same as in Example 1 to investigate the effect of reaction time on product yield. The results are listed in Table 3.

[0047] Table 3 Reaction conditions and reaction results of Examples 15 to 17

[0048] Example Reaction time / h Product separation yield (%) 15 8 54 16 16 85 17 24 97

[0049] Examples 18-19

[0050] The hydrogenolysis reaction of different polyesters was investigated using the ionic liquid [BMIm][Cl] of Example 1 as solvent and the same reaction conditions as Example 1. The results are listed in Table 4.

[0051] Table 4 Reaction conditions and results of Examples 1, 18, and 19

[0052] Example Polyester Carboxylic acid name and yield (%) 1 PET Terephthalic acid, 97 18 PPT Terephthalic acid, 93 19 PBT Terephthalic acid, 86

[0053] Examples 20 to 24

[0054] Use of organic solvent. Using an organic solvent can reduce the amount of ionic liquid required. Using the ionic liquid [BMIm][Cl] from Example 1 as the solvent, the amount was reduced to 0.5 mL. 1.5 mL of organic solvent was added to dissolve the PET. Using the same reaction conditions as Example 1, the hydrogenolysis reaction of PET was studied. The results are listed in Table 5.

[0055] Table 5 Reaction conditions and reaction results of Examples 20 to 24

[0056] Example organic solvents Yield (%) 1 none 97 20 Tetrahydrofuran 92 21 Acetonitrile 92 22 Chloroform 90 23 dichloromethane 88 24 1,4-Dioxane 93

[0057] Examples 25 to 36

[0058] Varying the type of heterogeneous metal catalyst. Using the ionic liquid [BMIm][Cl] from Example 1 as the solvent and the same reaction conditions as in Example 1, the effects of different metal catalysts (50 mg for a catalyst with a metal content of 5 wt%) on the hydrogenolysis of PET were investigated. The results are listed in Table 6.

[0059] Table 6 Reaction conditions and reaction results of Examples 25 to 36

[0060] Example Metal catalysts Terephthalic acid yield (%) 1 Pd / C 97 25 <![CDATA[Pd / TiO2]]> 93 26 Pd / montmorillonite (MMT) 86 27 Pt / C 85 28 Ru / C 86 29 Rh / C 95 30 Au / C 89 31 PdNi / C 96 32 <![CDATA[PtFe / TiO2]]> 95 33 RuNi / MMT 89 34 RhCo / C 93 35 AuCu / C 91 36 <![CDATA[PdCu / TiO2]]> 84

[0061] Examples 37 to 42

[0062] Homogeneous metal catalysts were used. The ionic liquid [BMIm][Cl] from Example 1 was used as the solvent, and the same reaction conditions as in Example 1 were employed to investigate the effects of different homogeneous metal catalysts on the hydrogenolysis of PET. The amount of active metal in the metal catalyst was 0.5 wt% based on the mass of the polymer. The results are listed in Table 7.

[0063] Table 7 Reaction conditions and reaction results of Examples 37 to 40

[0064] Example Homogeneous metal catalysts Terephthalic acid yield (%) 37 <![CDATA[PdCl2]]> 97 38 <![CDATA[Pd(CH3COO)2]]> 93 39 <![CDATA[Pd(acac)2]]> 86 40 <![CDATA[Ru3(CO) 12 ]]> 85 41 <![CDATA[Rh(acac)(CO)2]]> 86 42 <![CDATA[Rh2(CO)4Cl2]]> 90

Claims

1. Application of a catalyst system in the preparation of carboxylic acid by catalytic hydrogenolysis of polyester plastics; the catalyst system comprises an ionic liquid and a metal catalyst; The ionic liquid has a cation selected from imidazolyl cations, pyridyl cations, quaternary ammonium salts, quaternary phosphonium salts, HDBU, and HTMG, and an anion selected from halogen anions or halogen-containing Lewis anions. The metal catalyst is a homogeneous or heterogeneous metal catalyst having a hydrogenolysis function; The homogeneous metal catalyst having hydrogenolysis function is a compound containing at least one noble metal element of Pd, Ru, Pt, Au, and Rh; The heterogeneous metal catalyst with hydrogenolysis function is selected from: nanocatalysts with Pd, Ru, Pt, Au, Rh noble metals or bimetallic, multimetallic alloys or intermetallic compounds formed with Fe, Co, Ni, Cu, Mn non-noble metals as active ingredients.

2. The use according to claim 1, characterized in that In the catalytic system, the molar ratio of the ionic liquid to the active metal element in the metal catalyst is 10000:1-100.

3. The use according to claim 1, characterized in that: The polyester plastic is PET or PBT.

4. A method for preparing carboxylic acid by hydrogenolysis of polyester plastics, comprising the following steps: The polyester plastic is dissolved in an ionic liquid-based solvent, a metal catalyst is added, and the reaction is carried out under set temperature and pressure conditions to obtain polyester depolymerization products, carboxylic acid and alkane; The ionic liquid has a cation selected from imidazolyl cations, pyridyl cations, quaternary ammonium salts, quaternary phosphonium salts, HDBU, and HTMG, and an anion selected from halogen anions or halogen-containing Lewis anions. The metal catalyst is a homogeneous or heterogeneous metal catalyst having a hydrogenolysis function; The homogeneous metal catalyst having hydrogenolysis function is a compound containing at least one noble metal element of Pd, Ru, Pt, Au, and Rh; The heterogeneous metal catalyst with hydrogenolysis function is selected from: nanocatalysts with Pd, Ru, Pt, Au, Rh noble metals or bimetallic, multimetallic alloys or intermetallic compounds formed with Fe, Co, Ni, Cu, Mn non-noble metals as active ingredients.

5. The method according to claim 4, characterized in that: The ionic liquid-based solvent is a pure ionic liquid or a solvent system consisting of an ionic liquid and an organic solvent; The organic solvent is a solvent capable of dissolving polyester plastics, and is selected from any one or a mixture of the following: tetrahydrofuran, N,N-dimethylformamide, 1,4-dioxane, ether, acetonitrile, dichloromethane, and chloroform.

6. The method according to claim 4, characterized in that: The weight of the active metal element in the metal catalyst accounts for 0.1%-10% of the weight of the polyester plastic.

7. The method according to claim 4, characterized in that: The temperature range of the hydrogenolysis reaction is room temperature to 200° C.; the hydrogen pressure range is normal pressure to 10 MPa; and the reaction time is 2 to 24 h.

8. The method according to claim 4, wherein: The method further includes the operations of separating the carboxylic acid from the reaction system and recovering the ionic liquid and the metal catalyst; The separation steps are as follows: 1) separating the heterogeneous metal catalyst from the reaction system by filtration; then, based on the solubility characteristics of the ionic liquid and the carboxylic acid, selecting an antisolvent that is miscible with the ionic liquid but insoluble or slightly soluble in the carboxylic acid, adding the antisolvent to the reaction system to precipitate the carboxylic acid product, and filtering to separate the solid carboxylic acid; then, distilling the ionic liquid solution to remove the solvent, and recovering the ionic liquid for recycling; or 1') For homogeneous metal catalyst reaction systems, a suitable antisolvent is selected to precipitate the carboxylic acid from the reaction system, leaving the catalyst in the ionic liquid solution. The solid carboxylic acid is then separated by filtration. The ionic liquid solution containing the catalyst is then distilled to remove the solvent, and the ionic liquid-metal catalyst is recovered for recycling.

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