Method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics

Abstract

The present invention relates to the technical field of chemical recovery of polystyrene plastics, and specifically to a method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics, comprising the following steps: mixing a catalyst, a nitrogen source reagent, an additive and a solvent with polystyrene and then carrying out a depolymerization reaction; solid-liquid separation and washing; concentrating, alkalizing and extracting the obtained liquid to obtain an aqueous phase I and an organic phase I; acidifying the aqueous phase I and then extracting to obtain an organic phase III, thermally eluting the organic phase III, removing the solvent from the eluent and purifying to obtain benzoic acid; concentrating the organic phase I and then recrystallizing and purifying to obtain benzamide, solid-liquid separation to obtain an organic phase II, and removing the solvent to obtain benzonitrile. The method of the present invention has high degradation efficiency, and the product can be purified by simple separation means to obtain a pure product. The method has simple reaction conditions, is green and cheap, has a good yield, and has good wide applicability to polystyrene plastics.

Description

Technical Field

[0001] The invention relates to the technical field of chemical recovery of polystyrene plastics, and in particular to a method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics. Background Art

[0002] Polystyrene (PS) was first discovered in 1839. It is obtained by the polymerization of styrene monomers in the presence of catalysts or initiators according to free radical mechanisms or ionic mechanisms. Common types include ordinary polystyrene, expanded polystyrene (EPS), high-impact polystyrene (HIPS), etc. Polystyrene is now the fifth largest plastic produced in the world, but its recycling rate is less than 1%. Marine garbage, microplastics, white pollution, etc. are all related to it. At present, the common recycling method is mainly to re-granulate it through primary and secondary recycling to obtain recycled benzene particles. The second is to convert it into gas, benzene, toluene, ethylbenzene, styrene or benzoic acid and other products through chemical recycling using light, heat, microwaves, biology and other means.

[0003] Different from the above-mentioned methods, the present invention realizes the catalytic cracking of polystyrene through a simple and green method and obtains new product types. At the same time, the method has good applicability to polystyrene plastics. Summary of the invention

[0004] The object of the present invention is to provide a method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics, which can not only realize the catalytic depolymerization of polystyrene under a simple reaction system, but also obtain separable benzonitrile, benzamide and other high value-added depolymerization products by using a solvent as a nitrogen source.

[0005] The scheme adopted by the present invention to achieve the purpose is: a method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics, comprising the following steps:

[0006] (1) mixing a catalyst, a nitrogen source reagent, an additive, a solvent and a polystyrene plastic to perform a depolymerization reaction;

[0007] (2) after the reaction is completed, a solid-liquid mixture is obtained, the solid-liquid mixture is separated and washed with a polar organic solvent, and all the liquids are combined;

[0008] (3) concentrating the liquid obtained in step (2) and then alkalizing it, and then extracting the solution with a highly polar organic solvent to obtain an aqueous phase I and an organic phase I;

[0009] (4) After the aqueous phase I is acidified, it is extracted with a highly polar organic solvent to obtain an organic phase III. After the organic phase III is freed of solvent, it is hot eluted with a less polar organic solvent. The eluent is freed of solvent to obtain a crude benzoic acid product. The crude benzoic acid product is purified to obtain benzoic acid;

[0010] The organic phase I is dehydrated and then the solvent is removed. The obtained product is recrystallized to precipitate crude benzamide. The organic phase II is obtained by solid-liquid separation. The organic phase II is desolventized to obtain benzonitrile. The solid crude benzamide is purified to obtain pure benzamide.

[0011] Preferably, in step (1), the concentration of polystyrene in the mixed solution is 0.05-4.00 mol / L based on its styrene monomer, the catalyst accounts for 5%-20% of the molar concentration of the styrene monomer contained in the added polystyrene, the molar ratio of the nitrogen source reagent to the styrene monomer contained in the polystyrene is 1-100:1, and the additive accounts for 10%-20% of the molar concentration of the styrene monomer contained in the added polystyrene.

[0012] Preferably, in step (1), the catalyst includes at least one of homogeneous or heterogeneous copper salts, manganese salts, iron salts, cobalt salts, and nickel salts; the nitrogen source reagent includes at least one of acetonitrile, ammonia gas, ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium acetate, urea, N,N-dimethylformamide, and ammonium sulfate.

[0013] Preferably, in step (1), the additive includes at least one of sodium hydroxide, acetic acid, water, lithium iodide, calcium chloride, sodium sulfate, and sulfuric acid; and the solvent includes at least one of ethyl acetate, petroleum ether, acetone, 1,4-dioxane, tert-butanol, tert-amyl alcohol, acetic acid, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile.

[0014] Preferably, in step (1), the reaction conditions of the depolymerization reaction are: an oxygen-containing atmosphere with a pressure of 1.0-3.0 MPa, a reaction temperature of 140-200° C., and a reaction time of 5-15 h.

[0015] Preferably, in step (2), the polar organic solvent comprises at least one of ethyl acetate, acetone, acetonitrile, chloroform and methanol.

[0016] Preferably, in step (3), an aqueous solution of at least one of sodium hydroxide, potassium hydroxide and sodium carbonate is used for alkalization to a pH of 10-11, and the highly polar organic solvent includes at least one of ethyl acetate, dichloromethane and chloroform.

[0017] Preferably, in step (4), the acidification is performed using an aqueous solution of at least one of hydrogen chloride, sulfuric acid, and nitric acid to a pH of 3-4, and the highly polar organic solvent comprises at least one of ethyl acetate, dichloromethane, and chloroform; the less polar solvent comprises C5-C 18 Alkane-type small polar organic solvents or aromatic ring-type small polar organic solvents.

[0018] Preferably, n-hexane, n-pentane, isopentane, petroleum ether or kerosene, etc., are used. 18 Thermal elution is performed using small polar organic solvents such as alkanes or toluene.

[0019] Preferably, in step (4), petroleum ether or diethyl ether is used for recrystallization.

[0020] Preferably, the process also includes the recovery of the catalyst, and the specific operation is: washing the solid obtained in step (1), and then drying to obtain the recovered catalyst.

[0021] The present invention has the following advantages and beneficial effects:

[0022] The method of the present invention has high degradation efficiency, and the product can be purified by simple separation means to obtain a pure product. After the reaction is completed, the solid recovered can be used as a catalyst to complete the depolymerization of polystyrene and styrene copolymers again under the same reaction system conditions to produce benzonitrile, benzamide and benzoic acid. The method has simple reaction conditions, is green and cheap, has a good yield, and has good wide applicability to polystyrene plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A diagram of a partially degraded raw material used in the present invention;

[0024] Figure 2 This is a picture of the product prepared in Example 2;

[0025] Figure 3 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0026] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0027] The method of the present invention comprises the following steps:

[0028] (1) mixing a catalyst, a nitrogen source reagent, an additive, a solvent and polystyrene and adding them into a reactor for depolymerization;

[0029] (2) after the reaction is completed, a solid-liquid mixture is obtained, filtered, and washed with at least one of polar organic solvents such as ethyl acetate, acetone, acetonitrile, chloroform, and methanol;

[0030] (3) All products are located in the filtrate. The filtrate is collected by suction filtration and purified by a certain treatment method to obtain benzonitrile, benzoic acid and benzamide respectively;

[0031] The above-mentioned certain treatment method is: after the filtrate is concentrated by vacuum distillation, it is alkalized to a pH of 10 to 11 using at least one of common alkaline aqueous solutions such as sodium hydroxide, potassium hydroxide, sodium carbonate, etc., and the solution is extracted three times using an organic solvent (including but not limited to ethyl acetate, dichloromethane, chloroform and other highly polar organic solvents) to obtain an aqueous phase I and an organic phase I; the aqueous phase I is acidified to a pH of 3 to 4 using a common acidic aqueous solution such as hydrogen chloride, sulfuric acid, or nitric acid, and then an organic solvent (including but not limited to ethyl acetate, dichloromethane, chloroform and other highly polar organic solvents) is used. The solution was extracted three times with an organic solvent to obtain an organic phase III; after adding anhydrous sodium sulfate to dry the organic phase I, the organic phase I was concentrated by low-temperature vacuum distillation to remove the solvent, and petroleum ether or ether (boiling range: 30-60°C) was added to precipitate crude benzamide by recrystallization to obtain an organic phase II; the organic phase II was subjected to vacuum distillation to remove the solvent to obtain benzonitrile; the crude benzamide was subjected to secondary recrystallization (EA:PE=5:1) to obtain pure benzamide; the organic phase III was subjected to vacuum distillation to remove the solvent, and then the organic phase III was treated with n-hexane, n-pentane, isopentane, petroleum ether or kerosene and other C5-C 18 The alkane and toluene and other aromatic ring small polarity solvents are used for hot elution, and the eluent is distilled under reduced pressure to remove the solvent to obtain crude benzoic acid. The crude benzoic acid is dissolved in a small amount of hot water and then cooled in an ice bath for crystallization, and then filtered and dried to obtain benzoic acid;

[0032] (4) The solid phase filter cake obtained in step (2) is washed with ethyl acetate for 2-3 times, and then vacuum dried at 40° C. to obtain a recovery catalyst having a catalytic effect on the depolymerization of polystyrene; the above-mentioned catalytic effect on the depolymerization of polystyrene means that the recovery catalyst can depolymerize polystyrene under the conditions of the reaction system of the initial recovery scale without adding copper halide as a catalyst to obtain benzonitrile, benzamide and benzoic acid as products, wherein benzoic acid and benzamide are the main products.

[0033] In step (1), the concentration of polystyrene in the mixed system includes but is not limited to 0.05-4.00 mol / L (referring to the molar concentration of styrene monomer contained in polystyrene), the catalyst concentration includes but is not limited to 5%-20% (based on the molar amount of styrene monomer contained in the added polystyrene), the amount of nitrogen source reagent is 1 equivalent to 100 equivalents (based on the molar amount of styrene monomer contained in the added polystyrene), and the amount of additive is 10% to 20% (based on the molar amount of styrene monomer contained in the added polystyrene).

[0034] The catalyst is a homogeneous or heterogeneous copper, manganese, iron, cobalt, or nickel salt catalyst. The homogeneous catalyst includes but is not limited to manganese chloride, cupric chloride, cuprous chloride, cupric bromide, cuprous bromide, copper, cupric oxide, cuprous oxide, cupric acetate, manganese dioxide, cobalt tetraoxide, ferrous chloride, cobalt chloride, manganese bromide, nickel chloride, and the like and their corresponding hydrates; the heterogeneous catalyst includes but is not limited to MnO x , CuBr@C, CuBr@Al2O3, 5%Cu / Beta, 5%Cu / Al2O3 / 1N, 5%Cu / Al2O3 / 2N, CuO@CuBr, etc.

[0035] The additive includes at least one of sodium hydroxide, acetic acid, water, lithium iodide, calcium chloride, sodium sulfate, sulfuric acid, etc.

[0036] Nitrogen source reagents include but are not limited to acetonitrile, ammonia, ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium acetate, urea, N,N-dimethylformamide, ammonium sulfate, etc.; certain solvents include but are not limited to ethyl acetate, petroleum ether, acetone, 1,4-dioxane, tert-butanol, tert-amyl alcohol, acetic acid, N,N-dimethylformamide, dimethyl sulfoxide or acetonitrile, etc.

[0037] The preferred reaction solvent is acetonitrile, and the preferred reaction additive required by the reaction system is water, and the preferred volume ratio of water to acetonitrile is 2:25.

[0038] The reaction conditions of the depolymerization reaction are: an oxygen-containing atmosphere with a pressure of 1.0-3.0 MPa, a reaction temperature of 140-200° C., and a reaction time of 5-15 h.

[0039] In the present invention, the preferred temperature for catalytic oxidation degradation is 200° C., the preferred pressure is 2.0 MPa, and the preferred reaction time is 10 to 15 hours.

[0040] The oxygen-containing atmosphere used in the present invention may be pure oxygen or a mixture of oxygen and an inert gas (such as a gas mixture of oxygen and nitrogen) or air, etc. Preferably, the oxygen-containing atmosphere is a pure oxygen atmosphere.

[0041] In the present invention, the degradation substrate includes but is not limited to pure polystyrene, pure styrene copolymer, styrene and substituted styrene related polymers or other related product wastes.

[0042] The method of the invention uses homogeneous or heterogeneous copper, manganese, iron, cobalt, nickel salt as a catalyst, ethyl acetate, petroleum ether, acetone, 1,4-dioxane, tert-butyl alcohol, tert-amyl alcohol, acetic acid, N,N-dimethylformamide, dimethyl sulfoxide or acetonitrile as a reaction solvent, and acetonitrile, ammonia, ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium acetate, urea, N,N-dimethylformamide, ammonium sulfate and the like as a nitrogen source to oxidatively degrade pure polystyrene and styrene copolymers or waste products related thereto to produce benzonitrile, benzamide and benzoic acid under the conditions of a temperature of 140-200 DEG C and an oxygen or air pressure of 1.0-3.0MPa.

[0043] Example 1

[0044] Add 3.1200g of commercial polystyrene particles, 0.4290g (0.3mmol) of cuprous bromide and 60mL of acetonitrile to a quartz reaction bottle of a high-pressure reactor with a volume of 250mL, and add 4.8mL of water to the reaction mixture while stirring. Place the stirred reaction bottle in the reactor, introduce oxygen until the pressure value in the reactor is 2MPa, and the degradation reaction is reacted for 15h at a temperature of 200℃. After the reaction is completed, the vacuum filter is filtered, and the filter cake is washed 2 to 3 times with ethyl acetate to separate the reaction solid and liquid. The reaction yield is determined by gas chromatography, and the yield of benzonitrile is 39%, the yield of benzamide is 41%, and the yield of benzoic acid is 6%. Using the above-mentioned separation method, the actual separation yield of the product is obtained. That is, after the filtrate is concentrated by vacuum distillation, sodium hydroxide aqueous solution is added to alkalize to pH 10-11, and the solution is extracted three times with ethyl acetate to obtain aqueous phase I and organic phase I; aqueous phase I is acidified to pH 3-4 by adding hydrogen chloride aqueous solution to obtain aqueous phase II, and the solution is extracted three times with ethyl acetate to obtain organic phase III; organic phase I is dried by adding anhydrous sodium sulfate, concentrated by low-temperature vacuum distillation to remove the solvent, petroleum ether (boiling range: 30-60° C.) is added, crude benzamide is precipitated by recrystallization and organic phase II is obtained; organic phase II is distilled under reduced pressure to remove the solvent to obtain benzonitrile; the crude benzamide is recrystallized twice (EA:PE=5:1) to obtain pure benzamide; the ethyl acetate phase II is distilled under reduced pressure to remove the solvent, and then it is hot eluted with n-hexane 2-3 times, the eluent is distilled under reduced pressure to remove the solvent to obtain crude benzoic acid, the crude benzoic acid is dissolved in a small amount of hot water, cooled and crystallized, and filtered and dried to obtain benzoic acid. The actual separation yield of benzonitrile is 32%, the actual separation yield of benzamide is 38%, and the actual separation yield of benzoic acid is 6%.

[0045] The benzamide, benzoic acid and benzonitrile separated in this example 1 The H NMR data are as follows:

[0046] Benzamide

[0047]

[0048] Benzamide(1a): 1 H NMR (400MHz, Chloroform-d) δ7.81 (d, 2H), 7.53 (t, J = 7.4Hz, 1H),

[0049] 7.45(t,J=7.5Hz,2H),6.06(s,2H). 13 C NMR (101MHz, Chloroform-d) δ169.6, 133.5, 132.1, 128.71, 127.4.

[0050] Benzonitrile

[0051]

[0052] Benzonitrile(2a): 1 H NMR(400MHz,Chloroform-d)δ7.68–7.63(t,2H),7.60(t,J=7.6

[0053] Hz,1H),7.47(t,J=7.8Hz,2H). 13 C NMR (101MHz, Chloroform-d) δ 132.8, 132.2, 129.2, 118.9, 112.5.

[0054] benzoic acid

[0055]

[0056] Benzoic acid(3a): 1 H NMR(400MHz,Chloroform-d)δ8.14(d,2H),7.63(t,J=7.4Hz,1H),

[0057] 7.49 (t, J = 7.8 Hz, 2H). 13 C NMR (101MHz, Chloroform-d) δ172.5, 133.9, 130.3, 129.4, 128.6.

[0058] Example 2

[0059] The commercial polystyrene in Example 1 was replaced with foam, and the dosage and experimental steps were the same as above. The reaction yield was determined by gas chromatography, and the yield of benzonitrile was 30%, the yield of benzamide was 40%, and the yield of benzoic acid was 3%. After separation operation, the actual separation yield of benzonitrile was 30%, the actual separation yield of benzamide was 43%, and the actual separation yield of benzoic acid was 2%.

[0060] The actual product prepared in this embodiment is shown in the figure Figure 2 shown.

[0061] Example 3

[0062] The commercial polystyrene in Example 1 was replaced with a yogurt box, and the dosage and experimental steps were the same as above. The reaction yield was determined by gas chromatography, and the yield of benzonitrile was 29%, the yield of benzamide was 30%, and the yield of benzoic acid was 3%. After separation operation, the actual separation yield of benzonitrile was 23%, the actual separation yield of benzamide was 33%, and the actual separation yield of benzoic acid was 2%.

[0063] Example 4

[0064] The commercial polystyrene in Example 1 was replaced by polystyrene maleic anhydride copolymer, wherein the amount of polystyrene maleic anhydride copolymer (homopolymer) was 6.0644 g, and the remaining amounts and experimental steps were the same as above. The reaction yield was determined by gas chromatography, and the yield of benzonitrile was 14%, the yield of benzamide was 27%, and the yield of benzoic acid was 13%. After separation operation, the actual separation yield of benzonitrile was 14%, the actual separation yield of benzamide was 24%, and the actual separation yield of benzoic acid was 11%.

[0065] Example 5

[0066] The commercial polystyrene in Example 1 was replaced by a polystyrene acrylonitrile copolymer, wherein the amount of the polystyrene acrylonitrile copolymer (acrylonitrile: 25 w.t.%) was 4.1600 g, and the remaining amounts and experimental steps were the same as above. The reaction yields were determined by gas chromatography, and the yields of benzonitrile, benzamide, and benzoic acid were 27%, 41%, and 4%, respectively. After separation operation, the actual separation yields of benzonitrile, benzamide, and benzoic acid were 27%, 48%, and 3%, respectively.

[0067] Example 6

[0068] The cuprous bromide in Example 1 was replaced by the filter cake obtained by suction filtration and drying under the reaction conditions of Example 1, and all of it was used as the recovered solid catalyst for the reaction, and the remaining amounts and experimental steps were the same as above. The reaction yield was determined by gas chromatography, and the yield of benzonitrile was 21%, the yield of benzamide was 19%, and the yield of benzoic acid was 26%.

[0069] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics, characterized in that: The following steps are involved: (1) Mixing a catalyst, a nitrogen source reagent, an additive, a solvent and a polystyrene plastic to perform a depolymerization reaction; (2) After the reaction is completed, a solid-liquid mixture is obtained, the solid and liquid are separated and washed with a polar organic solvent, and all liquids are combined. The polar organic solvent includes at least one of ethyl acetate, acetone, acetonitrile, chloroform, and methanol; (3) the liquid obtained in step (2) is concentrated and then alkalized, and then the solution is extracted with a highly polar organic solvent to obtain an aqueous phase I and an organic phase I, wherein the highly polar organic solvent comprises at least one of ethyl acetate, dichloromethane, and chloroform; (4) After the aqueous phase I is acidified, it is extracted with a highly polar organic solvent to obtain an organic phase III. After the organic phase III is desolventized, it is hot eluted with a less polar organic solvent. The eluent is desolventized to obtain a crude benzoic acid product. The crude benzoic acid product is purified to obtain benzoic acid. The highly polar organic solvent includes at least one of ethyl acetate, dichloromethane, and chloroform; the less polar solvent includes C5-C 18 Alkane-type small polar organic solvents or aromatic ring-type small polar organic solvents; The organic phase I is dehydrated and then the solvent is removed, the obtained product is recrystallized to precipitate crude benzamide, solid-liquid separation is performed to obtain an organic phase II, the organic phase II is desolventized to obtain benzonitrile, and the solid crude benzamide is purified to obtain pure benzamide; In the step (1), the catalyst includes at least one of homogeneous or heterogeneous copper salts, manganese salts, iron salts, cobalt salts, and nickel salts; the nitrogen source reagent includes at least one of acetonitrile, ammonia, ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium acetate, urea, N,N-dimethylformamide, and ammonium sulfate; the additive includes at least one of sodium hydroxide, acetic acid, water, lithium iodide, calcium chloride, sodium sulfate, and sulfuric acid; the solvent includes at least one of ethyl acetate, petroleum ether, acetone, 1,4-dioxane, tert-butyl alcohol, tert-amyl alcohol, acetic acid, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile; the reaction conditions of the depolymerization reaction are: an oxygen-containing atmosphere with a pressure of 1.0-3.0 MPa, a reaction temperature of 140-200° C., and a reaction time of 5-15 h.

2. The method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics according to claim 1, characterized in that: In the step (1), the concentration of polystyrene in the mixed solution is 0.05-4.00 mol / L based on its styrene monomer, the catalyst accounts for 5%-20% of the molar concentration of the styrene monomer contained in the added polystyrene, the molar ratio of the nitrogen source reagent to the styrene monomer contained in the polystyrene is 1-100:1, and the additive accounts for 10%-20% of the molar concentration of the styrene monomer contained in the added polystyrene.

3. The method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics according to claim 1, characterized in that: In the step (3), an aqueous solution of at least one of sodium hydroxide, potassium hydroxide and sodium carbonate is used for alkalization to a pH of 10-11.

4. The method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics according to claim 1, characterized in that: In the step (4), the solution is acidified with an aqueous solution of at least one of hydrogen chloride, sulfuric acid and nitric acid to a pH of 3-4.

5. The method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics according to claim 1, characterized in that: In the step (4), petroleum ether or diethyl ether is used for recrystallization.

6. The method for producing benzonitrile, benzamide and benzoic acid by catalytic oxidative depolymerization of polystyrene and styrene copolymer plastics according to claim 1, characterized in that: The method also includes the recovery of the catalyst, and the specific operation is: washing the solid obtained in step (1) and drying it to obtain the recovered catalyst.

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