Method for producing benzoic acid by taking waste plastic as raw material

Abstract

The invention discloses a method for producing benzoic acid by taking waste plastic as a raw material, and relates to the technical field of waste plastic high-valued treatment. The method comprises the following steps: mixing waste plastic and a catalyst in an oxygen-containing atmosphere for reaction to obtain a benzoic acid monomer; the waste plastic at least comprises polystyrene; the catalyst comprises at least one of a single metal oxide, a composite metal oxide and a supported metal oxide. The invention provides a chemical method for converting waste plastics into high-value benzoic acid, and solves a series of problems of harsh chemical conversion conditions, complex products, difficult separation, low added value and the like of the existing waste plastics. The benzoic acid obtained by the invention can be applied to production of food additives, essence and plastic monomers, and high-valued and green circulation of waste plastics is realized.

Description

Technical Field

[0001] The invention relates to the technical field of high-value waste plastics, and in particular to a method for producing benzoic acid using waste plastics as raw materials. Background Art

[0002] With the continuous development of society, human demand for plastic products is increasing. However, about 80% of plastics are not properly treated or recycled after use, and are discarded in landfills or directly released into the environment. Since most plastics are difficult to degrade in the natural environment, a large amount of solid waste is formed, and some are transformed into microplastics that are more difficult to handle. This not only threatens environmental safety and human health, but also causes a serious waste of carbon-containing resources. At present, there is an urgent need to design reasonable methods to recycle, upgrade and reuse plastic waste to cope with a series of energy and environmental crises.

[0003] There are many types of plastic waste, among which polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and polyethylene terephthalate (PET) account for more than 70% of all plastic waste. Although traditional mechanical recycling and incineration methods can recover some plastics and energy, the performance of the recycled plastics is significantly reduced, and highly toxic pollutants such as dioxins are easily produced during the incineration process, which increases the environmental burden. Although waste plastics can be converted into liquid fuels or chemical monomers through chemical methods such as pyrolysis or hydrogenolysis. However, the reaction conditions are often harsh, the products are complex and difficult to separate. Therefore, developing a method for oxidative upgrading of waste plastics under mild conditions to convert waste plastics into higher-value oxygen-containing products is not only conducive to enriching the chemical methods for high-value waste plastics, but also provides a solution to the problem of environmental solid waste pollution.

[0004] Benzoic acid is the simplest aromatic acid, mainly used to prepare sodium benzoate preservatives, and used in the synthesis of drugs and dyes. It is also used to make plasticizers, mordants, fungicides and fragrances. In industry, it is mainly prepared by direct oxidation of toluene in the presence of manganese dioxide, or by decarboxylation of phthalic anhydride with water vapor. It is technically difficult to convert PS or mixed plastics containing PS into benzoic acid monomers. It is necessary to ensure that the catalyst activity can oxidatively break the CC bond on the polystyrene main chain, and to avoid oxidation or deep oxidation of the CH bond on the benzene ring to affect the selectivity of the product. Although there are a small number of reports on the conversion of PS or mixed plastics containing PS into benzoic acid, they are mainly homogeneous photocatalytic systems, and there are still a series of problems such as low product selectivity and difficulty in catalyst separation. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned problems in the prior art and to provide a method for producing benzoic acid using waste plastics as raw materials, so as to solve a series of problems in the existing waste plastic chemical conversion methods, such as harsh conditions, complex products, difficult separation, and low added value.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for producing benzoic acid using waste plastics as raw materials, comprising mixing the waste plastics and a catalyst in an oxygen-containing atmosphere to react and obtaining benzoic acid monomers; the waste plastics at least include polystyrene; the waste plastics also include at least one of polyethylene, polypropylene, and polyethylene terephthalate; the catalyst includes at least one of a single metal oxide, a composite metal oxide, and a supported metal oxide.

[0008] The single metal oxide includes at least one of TiO2, V2O5, Fe2O3, FeO, Fe3O4, NiO, CuO, ZnO, MoO3, La2O3, Nd2O3, Sm2O3, Er2O3, and WO3; preferably V2O5 and Fe2O3;

[0009] The composite metal oxide includes FeLaO x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x At least one of; preferably FeCeO x ;

[0010] The supported metal oxide includes at least one of Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2, Fe2O3 / CeO2, V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2, and V2O5 / CeO2; preferably, V2O5 / TiO2 and Fe2O3 / CeO2 catalysts.

[0011] In the reaction of the present invention, solvent water may be added or no solvent may be added; the oxygen-containing atmosphere may be oxygen or air; the mass fraction of the polystyrene in the waste plastics is 10% to 100%.

[0012] The reaction temperature of the present invention is 160-220° C., the reaction time is 1-12 h, the reaction pressure is 0.1-3 MPa, and the reaction stirring speed is 100-800 rpm; preferably 180-200° C., 8-10 h, 0.5-1.5 MPa, 300-500 rpm.

[0013] The preparation of the composite metal oxide comprises the following steps:

[0014] According to a certain proportion, La(NO3)3·6H2O, Ce(NO3)2·4H2O, Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Cr(NO3)3·9H2O and Fe(NO3)3·9H2O were respectively prepared into a solution of a certain concentration, and K2CO3 solution was used as a precipitant. The pH was adjusted at room temperature, and the obtained precipitate was aged at room temperature, filtered, washed, and dried overnight, and then calcined to obtain the catalyst FeLaO x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x .

[0015] Preferably, the concentration of the La(NO3)3·6H2O, Ce(NO3)2·4H2O, Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, and Cr(NO3)3·9H2O solutions is 0.1-1 mol / L; the concentration of the Fe(NO3)3·9H2O solution is 0.1-1 mol / L; the concentration of the KCO3 solution is 0.5-1 mol / L; the pH is 8-10; the aging time is 2-8 h; the drying temperature is 80-120°C, and the drying time is 6-12 h; the calcination temperature is 400-700°C, and the calcination time is 3-6 h.

[0016] The preparation of the supported metal oxide comprises the following steps:

[0017] Al2O3, SiO2, TiO2, ZrO2 and CeO2 carriers were impregnated in Fe(NO3)3·9H2O or NH4VO3 solutions, respectively. After impregnation, Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2, Fe2O3 / CeO2, V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2 and V2O5 / CeO2 catalysts were obtained after drying and calcination.

[0018] Preferably, the concentration of the Fe(NO3)3·9H2O and NH4VO3 solution is 0.005-0.1 mol / L; the impregnation time is 0.5-12 h; the drying temperature is 60-120°C, and the drying time is 6-12 h; the calcination temperature is 300-700°C, and the calcination time is 3-6 h; in Fe2O3 / CeO2, the mass fraction of Fe is 1%-5%; in V2O5 / TiO2, the mass fraction of V is 1%-10%.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1. The method for producing benzoic acid using waste plastics as raw materials provided by the present invention uses cheap and readily available metal oxides as catalysts, does not require solvents or uses water as a solvent, does not add inorganic acids, alkalis or organic solvents to the system, does not require precious metals, does not consume hydrogen, has mild reaction conditions, and has low process costs.

[0021] 2. The V2O5 / TiO2 and Fe2O3 / CeO2 catalysts are simple to prepare and have suitable oxygen vacancies, which can better activate oxygen in the atmosphere and contribute to the oxidative depolymerization of waste plastics. The unsaturated metal sites are conducive to the selective activation of CH bonds in waste plastics, thereby improving the selectivity of the product.

[0022] 3. The method for producing benzoic acid using waste plastics as raw materials provided by the present invention can convert polystyrene or a mixed plastic of polystyrene and one or more of polyethylene, polypropylene and polyethylene terephthalate into benzoic acid monomers in one step. The obtained benzoic acid can be used in the production of food additives, flavors, and plastic monomers, realizing the high value of waste plastics and green recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FeCeO prepared in Examples 2, 10, and 13 x , XRD patterns of Fe2O3 / CeO2 and V2O5 / TiO2.

[0024] Figure 2 14 is the chromatogram of the reaction product of Example 10.

[0025] Figure 3 This is the mass spectrum of the reaction product of Example 10. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0027] Embodiments 1 to 5

[0028] FeLaO of Examples 1 to 5 x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x The preparation method of the catalyst is as follows:

[0029] 0.5 mol / L La(NO3)3·6H2O, Ce(NO3)2·6H2O, Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Cr(NO3)3·9H2O solutions were mixed and stirred evenly with 0.5 mol / L Fe(NO3)3·9H2O solution, and the pH was adjusted to 9 at room temperature with 1 mol / L KCO3 solution. The obtained solution was aged at room temperature for 4 h, filtered, washed, dried at 120°C overnight, and finally calcined at 400°C for 3 h to obtain FeLaO x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x catalyst.

[0030] Embodiments 6 to 10

[0031] The preparation methods of the Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2, and Fe2O3 / CeO2 catalysts of Examples 6 to 10 are as follows:

[0032] Al2O3, SiO2, TiO2, ZrO2 and CeO2 carriers were impregnated in 0.02 mol / L Fe(NO3)3·9H2O solution, respectively. After being stirred for 3 h, they were dried at 100°C for 6 h and finally calcined at 500°C for 4 h to obtain Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2 and Fe2O3 / CeO2 catalysts with Fe mass fraction of 5%, respectively.

[0033] Examples 11 to 15

[0034] The preparation methods of the V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2, and V2O5 / CeO2 catalysts of Examples 11 to 15 are as follows:

[0035] Al2O3, SiO2, TiO2, ZrO2 and CeO2 carriers were impregnated in 0.005 mol / L NH4VO3 solution, stirred for 2 h, dried at 80 °C for 10 h, and finally calcined at 400 °C for 5 h to obtain V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2 and V2O5 / CeO2 catalysts with V mass fraction of 1%, respectively.

[0036] Embodiments 16 to 26

[0037] Examples 16 to 26 use commercial TiO2, V2O5, Fe2O3, FeO, Fe3O4, NiO, CuO, ZnO, MoO3, La2O3, and WO3.

[0038] Embodiments 1 to 26 The method for producing benzoic acid using waste plastics as raw materials is as follows:

[0039] In the absence of solvent, the waste plastic PS and the catalyst are directly mixed and dispersed in a 100 mL autoclave, and reacted for 10 hours at a temperature of 180°C, an oxygen pressure of 1 MPa, and a stirring rate of 500 rpm. After the reaction, the obtained product is dissolved, filtered, and collected with ethanol, and the filtrate obtained by filtration is distilled under reduced pressure at 40°C to obtain benzoic acid monomer. Table 1 shows the method parameters and performance results of producing benzoic acid using waste plastics as raw materials in Examples 1 to 26.

[0040] The product type and yield of benzoic acid monomer were tested as follows:

[0041] The test was conducted by using a 7890A gas chromatography-mass spectrometer from Agilent, USA. The liquid product of the obtained benzoic acid monomer was qualitatively and quantitatively analyzed in a gas chromatograph, the injection port temperature was 280°C, the column oven was kept at 80°C for 5min, then the temperature was raised to 260°C at a heating rate of 5°C / min for 15min, the chromatographic column was a Restek RTX-5Sil capillary column (the chromatographic column was 30m long and 0.0.25mm in diameter), the film thickness was 0.25μm, the chromatographic column carrier gas was He gas, the column flow rate was 0.5mL / min, the detector was a FID detector, and the detector temperature was 250°C. Product yield = m (product) / m (raw material) × 100%, wherein m (product) and m (raw material) are respectively the molar mass (mol) of the product quantitatively measured in the gas chromatograph and the molar mass (mol) of the polystyrene in the waste plastic added before the reaction. The results are shown in Tables 1 and 2.

[0042] The FeCeO x, Fe2O3 / CeO2 and V2O5 / TiO2 catalysts were characterized by X-ray powder diffractometer. Figure 1 shown.

[0043] The benzoic acid product obtained in Example 10 was dissolved in an ethanol solution and analyzed by chromatography-mass spectrometry using an Agilent 7890A gas chromatography system. The results are as follows: Figure 2 and Figure 3 shown.

[0044] Table 1

[0045] catalyst Benzoic acid yield catalyst Benzoic acid yield Example 1 <![CDATA[FeLaO x ]]> 38％ Embodiment 18 <![CDATA[Fe2O3]]> 42％ Example 2 <![CDATA[FeCeO x ]]> 61％ Embodiment 19 FeO 21％ Example 3 <![CDATA[FeMnO x ]]> 42％ Embodiment 20 <![CDATA[Fe3O4]]> 38％ Example 4 <![CDATA[FeCuO x ]]> 47％ Embodiment 21 NiO 17％ Example 5 <![CDATA[FeCrO x ]]> 51％ Embodiment 22 CuO 12％ Example 6 <![CDATA[Fe2O3 / Al2O3]]> 37％ Embodiment 23 ZnO 9％ Example 7 <![CDATA[Fe2O3 / SiO2]]> 40％ Embodiment 24 <![CDATA[MoO3]]> 21％ Example 8 <![CDATA[Fe2O3 / TiO2]]> 35％ Embodiment 25 <![CDATA[La2O3]]> 37％ Example 9 <![CDATA[Fe2O3 / ZrO2]]> 42％ Embodiment 26 <![CDATA[WO3]]> 29％ Example 10 <![CDATA[Fe2O3 / CeO2]]> 70％ Comparative Example 1 <![CDATA[Fe2O3 / CeO2]]> 55％ Embodiment 11 <![CDATA[V2O5 / Al2O3]]> 30％ Comparative Example 2 <![CDATA[Fe2O3 / CeO2]]> 40％ Example 12 <![CDATA[V2O5 / SiO2]]> 27％ Comparative Example 3 <![CDATA[Fe2O3 / CeO2]]> 0 Example 13 <![CDATA[V2O5 / TiO2]]> 41％ Comparative Example 4 <![CDATA[Fe2O3 / CeO2]]> 2％ Embodiment 14 <![CDATA[V2O5 / ZrO2]]> 29％ Comparative Example 5 <![CDATA[V2O5 / TiO2]]> 48％ Embodiment 15 <![CDATA[V2O5 / CeO2]]> 38％ Comparative Example 6 <![CDATA[V2O5 / TiO2]]> 45％ Example 16 <![CDATA[TiO2]]> 15％ Comparative Example 7 <![CDATA[V2O5 / TiO2]]> 22％ Embodiment 17 <![CDATA[V2O5]]> 36％ Comparative Example 8 <![CDATA[V2O5 / TiO2]]> 1％

[0046] Embodiment 27

[0047] Example 27 is a catalytic reaction carried out under the condition of using solvent water. Specifically, the waste plastic PS and the catalyst Fe2O3 / SiO2 are dispersed in 10 mL of water and then placed in a 100 mL high pressure reactor. The remaining reaction parameters are the same as those of 1 to 26. The performance results are shown in Table 2.

[0048] Embodiments 28 to 34

[0049] In Examples 28 to 34, the catalyst is Fe2O3 / SiO2, the raw material is a mixed waste plastic of PS and one or more of PE, PP, and PET, and the other reaction parameters are the same as those of Examples 1 to 26. For specific parameters and performance results, see Table 2.

[0050] Comparative Examples 1 to 8 are prepared by changing the catalyst and the reaction conditions. Please refer to the performance results in Table 1 for details.

[0051] The difference between Comparative Example 1 and Example 10 is that the calcination temperature of the Fe2O3 / CeO2 catalyst is 700° C. When a higher calcination temperature is used, the oxygen vacancy concentration of the Fe2O3 / CeO2 catalyst decreases, and the catalytic performance of converting waste plastics into benzoic acid monomers decreases.

[0052] The difference between Comparative Example 2 and Example 10 is that the mass fraction of Fe in the Fe2O3 / CeO2 catalyst is 1%. When a lower Fe loading is used, the catalytic activity of the Fe2O3 / CeO2 catalyst is lower, and the yield of converting waste plastics into benzoic acid monomers decreases.

[0053] The difference between Comparative Example 3 and Example 10 is that the reaction temperature is 160° C. When the reaction temperature is reduced to 160° C., the yield of the Fe2O3 / CeO2 catalyst in the reaction of converting waste plastics into benzoic acid monomers is zero.

[0054] The difference between Comparative Example 4 and Example 10 is that the O2 pressure is 0.1 MPa. When the O2 pressure is reduced to 0.1 MPa, the yield of the Fe2O3 / CeO2 catalyst in the reaction of converting waste plastics into benzoic acid monomers is very low.

[0055] The difference between Comparative Example 5 and Example 13 is that the calcination temperature of V2O5 / TiO2 is 700° C. When a higher calcination temperature is used, the catalytic performance of the V2O5 / TiO2 catalyst in converting waste plastics into benzoic acid monomers is slightly improved.

[0056] The difference between Comparative Example 6 and Example 13 is that the mass fraction of V in the V2O5 / TiO2 catalyst is 10%. When a higher V loading is used, the catalytic activity of the V2O5 / TiO2 catalyst does not change much, and the yield of converting waste plastics into benzoic acid monomers is slightly increased.

[0057] The difference between Comparative Example 7 and Example 13 is that the reaction temperature is 160° C. When the reaction temperature is reduced to 160° C., the yield of the V2O5 / TiO2 catalyst in the reaction of converting waste plastics into benzoic acid monomers is low.

[0058] The difference between Comparative Example 8 and Example 13 is that the O2 pressure is 0.1 MPa. When the O2 pressure is reduced to 0.1 MPa, the yield of the V2O5 / TiO2 catalyst in the reaction of converting waste plastics into benzoic acid monomers is very low.

[0059] Table 2

[0060] Example catalyst Waste plastic PS mass fraction (%) Solvents Benzoic acid yield Embodiment 27 <![CDATA[Fe2O3 / SiO2]]> PS 100 water 75％ Embodiment 28 <![CDATA[Fe2O3 / SiO2]]> PS+PE 50 none 65％ Embodiment 29 <![CDATA[Fe2O3 / SiO2]]> PS+PP 50 none 67％ Embodiment 30 <![CDATA[Fe2O3 / SiO2]]> PS+PET 50 none 72％ Embodiment 31 <![CDATA[Fe2O3 / SiO2]]> PS+PE+PP 20 none 68％ Embodiment 32 <![CDATA[Fe2O3 / SiO2]]> PS+PP+PE+PET 10 none 70％ Embodiment 33 <![CDATA[Fe2O3 / SiO2]]> PS+PP+PE+PET 30 none 73％ Embodiment 34 <![CDATA[Fe2O3 / SiO2]]> PS+PP+PE+PET 50 none 73％

[0061] As can be seen from the table, the present invention can convert PS or PS and one or more of PE, PP, and PET waste plastics into benzoic acid through a one-step reaction, and the yield of benzoic acid obtained by the method of the present invention is high. Benzoic acid can be used in the production of food additives, flavors, and plastic monomers, realizing the high value and green recycling of waste plastics.

Claims

1. A method for producing benzoic acid using waste plastics as raw materials, characterized in that: The waste plastic and the catalyst are mixed and reacted in an oxygen-containing atmosphere to obtain benzoic acid monomer; the waste plastic includes at least polystyrene; and the catalyst includes at least one of a single metal oxide, a composite metal oxide, and a supported metal oxide.

2. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1, characterized in that: The waste plastics also include at least one of polyethylene, polypropylene and polyethylene terephthalate.

3. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1, characterized in that: The mass fraction of polystyrene in waste plastics is 10% to 100%.

4. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1, characterized in that: The reaction temperature is 160-220°C, and the reaction pressure is 0.1-3MPa.

5. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1, characterized in that: The reaction may be carried out with or without the addition of water as a solvent; the oxygen-containing atmosphere may be oxygen or air.

6. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1, characterized in that: The single metal oxide includes at least one of TiO2, V2O5, Fe2O3, FeO, Fe3O4, NiO, CuO, ZnO, MoO3, La2O3, Nd2O3, Sm2O3, Er2O3, and WO3; the composite metal oxide includes FeLaO x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x At least one of the following: the supported metal oxide includes at least one of Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2, Fe2O3 / CeO2, V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2, and V2O5 / CeO2.

7. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1 or 6, characterized in that: The preparation of the composite metal oxide comprises the following steps: respectively preparing La(NO3)3·6H2O, Ce(NO3)2·4H2O, Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Cr(NO3)3·9H2O and Fe(NO3)3·9H2O into a solution, using a K2CO3 solution as a precipitant, adjusting the pH at room temperature, aging the obtained precipitate at room temperature, filtering, washing, and drying, and then calcining to obtain a catalyst FeLaO x 、FeCeO x 、FeMnO x 、FeCuO x 、FeCrO x .

8. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 1 or 6, characterized in that: The preparation of the supported metal oxide comprises the following steps: impregnating Al2O3, SiO2, TiO2, ZrO2 and CeO2 carriers in Fe(NO3)3·9H2O or NH4VO3 solution respectively, and obtaining Fe2O3 / Al2O3, Fe2O3 / SiO2, Fe2O3 / TiO2, Fe2O3 / ZrO2, Fe2O3 / CeO2, V2O5 / Al2O3, V2O5 / SiO2, V2O5 / TiO2, V2O5 / ZrO2 and V2O5 / CeO2 after the impregnation is completed, drying and calcining.

9. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 8, characterized in that: The calcination temperature is 300-700°C.

10. A method for producing benzoic acid using waste plastics as raw materials as claimed in claim 8, characterized in that: In Fe2O3 / CeO2, the mass fraction of Fe is 1% to 5%; in V2O5 / TiO2, the mass fraction of V is 1% to 10%.

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