Method for recovering mixed organic acid from waste polyolefin plastic

Abstract

The invention discloses a method for recovering mixed organic acid from waste polyolefin plastics, which comprises the following steps: a, mixing the waste polyolefin plastics with an oxidizing agent and a catalyst, and carrying out oxidation reaction; and b, separating the reaction product through reduced pressure distillation to obtain the mixed organic carboxylic acid. The method has the advantages that the reaction conditions are relatively mild, the raw material application range is wide, the catalyst is easy to separate and can be recycled, and efficient conversion from the waste plastics to the resource product organic acid can be realized.

Description

Technical Field

[0001] The invention belongs to the field of plastic recycling, and in particular relates to a method for recycling mixed organic acids from waste polyolefin plastics. Background Art

[0002] Polyolefin plastics are currently the most widely used type of plastics due to their excellent properties such as easy processing, low price and outstanding performance. However, due to their extremely high chemical stability, they are difficult to degrade naturally, and the consumption of polyolefin plastics is still increasing year by year. Improper handling will cause serious "white" pollution and "microplastic" problems, so it is necessary to recycle and reuse waste plastics.

[0003] The methods of polyolefin degradation, conversion and recycling mainly include physical and chemical methods. The physical method mainly converts waste polyolefin plastics into low-quality recycled plastics through physical processes. It is relatively simple and easy, but it will lead to problems such as reduced polymer molecular weight and performance degradation. The chemical method is to obtain the monomers required for synthetic plastics through degradation and recycling, and then regenerate plastics and other valuable chemicals through a series of chemical reactions, thus realizing the recycling of polyolefins.

[0004] Physical recycling of polyolefins has low operating costs and requires less specialized technology, so it accounts for more than 75% of all recycling operations. However, the application of recycled plastics from physical recycling is narrow, which further leads to the continued increase in global plastic waste production. Therefore, research and development of efficient chemical recycling and reuse methods is a hot issue in industry research.

[0005] Chinese patent CN115322803B uses a solid acid catalyst to convert waste plastics into high value-added hydrocarbons at a relatively low temperature, but this process has problems such as catalyst carbon deposition and a narrow application path for the reaction products.

[0006] Therefore, seeking a mild process with high product added value to degrade and refine waste plastics is one of the keys to improving waste plastic recycling. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a method for recovering mixed organic acids from waste polyolefin plastics. The method has the advantages of relatively mild reaction conditions, high added value of reaction products, easy separation of catalysts, and reusability, and can achieve efficient conversion from waste plastics to resource-based products, organic acids.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for recovering mixed organic acids from waste polyolefin plastics comprises the following steps:

[0010] a. Add waste polyolefin plastics into a reactor, add oxidants and catalysts to make the waste plastics undergo oxidation reaction and decompose them into mixed organic matter containing carboxyl groups.

[0011] b. Separate the reaction product of step a by vacuum distillation to obtain a mixed organic carboxylic acid.

[0012] In the present invention, the sources of waste polyolefin plastics include but are not limited to plastic films, foams, packaging bags, cling films and other polyolefin products, wherein the polyolefin component includes polyethylene, polypropylene or a mixture thereof, preferably polyethylene.

[0013] Furthermore, polyethylene includes one or more of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-high molecular weight polyethylene (UHMWPE).

[0014] The polypropylene may be selected from one or more of homopolypropylene, copolymer polypropylene and the like.

[0015] Furthermore, in step a, the oxidant is selected from HNO 3 、N 2 O, NO, NO 2 , H 2 O 2 , O 2 , O 3 One or more of, preferably HNO 3 .

[0016] Furthermore, the mass ratio of the oxidant to the waste polyolefin plastic is 4:1-20:1.

[0017] Furthermore, in step a, the catalyst is copper nitrate, alumina, zeolite, SiO 2 One or more of the catalysts; the amount of catalyst added is 0.1%-10% of the mass of the waste polyolefin plastic, preferably 1%-5%.

[0018] Furthermore, in step a, the reaction temperature is 100-180° C., the reaction pressure is 3-10 MPa(A), and the reaction time is 1-10 h.

[0019] Furthermore, the carboxyl-containing mixed organic matter obtained in step a includes one or more of succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid and other organic carboxylic acids.

[0020] Furthermore, the temperature of the reduced pressure distillation in step b is 110-160° C., and the reaction pressure is 10-50 KPa(A).

[0021] Furthermore, the mixed organic carboxylic acid obtained in step b can be subsequently refined and separated to obtain different products.

[0022] Since waste polyolefin plastics have different sources and morphologies, in existing processes, they generally undergo physical pretreatment, such as cleaning and decomposition, before subsequent recycling reactions.

[0023] In some preferred technical solutions of the present invention, in order to better carry out the subsequent oxidation reaction, a chemical pretreatment operation is also included before the waste polyolefin plastic is subjected to step a.

[0024] Furthermore, the chemical pretreatment operation is specifically as follows: the waste polyolefin plastic is continuously transported to a thermal cracking reaction unit, and a thermal cracking reaction is carried out at 300-500° C. in an inert gas atmosphere with a reaction residence time of 1-2 hours to generate polyolefin wax.

[0025] In some preferred technical solutions of the present invention, the polyolefin wax obtained by pretreatment is subjected to steps a and b to obtain a mixed organic carboxylic acid.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The process technology has a wide range of applications and low requirements on the types of raw materials. It can be used for the recycling of common PP, PE plastics and their mixtures in life.

[0028] (2) Compared with thermal cracking and catalytic cracking recovery processes, this process is relatively simple, has low energy consumption, does not need to consider carbon deposition and catalyst recovery problems, and has a high yield of organic acid.

[0029] (3) The added value of the recovered products is high, and the proportion of the recovered dicarboxylic acid products is high. They can be further refined and separated for the preparation of different products. For example, succinic acid and adipic acid can be used as the main raw materials to be further converted into degradable plastics, and the higher fatty acids in the by-products can be used to make products such as soap. DETAILED DESCRIPTION

[0030] The present invention is further described below by means of specific examples, which are only used to illustrate the present invention and do not limit the scope of the present invention. The wt% in the examples represents the mass fraction.

[0031] (1) Sources of main raw materials in the embodiments of the present invention

[0032] Polyethylene (HDPE / LDPE / LLDPE) and polypropylene come from Wanhua Chemical's polyolefin unit;

[0033] HNO 3 , copper nitrate, SiO 2 : Purchased from Sinopharm Chemical Reagent Co., Ltd.

[0034] (2) Main analysis and testing methods

[0035] Excess methanol was added to the mixed organic acid product obtained in each embodiment and comparative example, and methylation was carried out at 70° C. The reaction time was 2 h. After methylation, qualitative analysis was performed using gas chromatography-mass spectrometry (GC-MS), and the organic acid content of the product was quantitatively analyzed in combination with standard samples such as dimethyl succinate, dimethyl glutarate, dimethyl adipate, dimethyl pimelate, dimethyl suberate, dimethyl azelaic acid, and dimethyl sebacate.

[0036] [Example 1]

[0037] Pretreatment: 100 g of high-density polyethylene (HDPE) was transported to a thermal cracking reactor and thermally cracked in a nitrogen atmosphere with a nitrogen flow rate of 50 ml / min, a thermal cracking temperature of 450°C, and a reaction time of 2 h. After the reaction, polyethylene wax was collected and the yield of polyethylene wax was 94%.

[0038] a. Take 10g of polyethylene wax and add it to the reactor. At the same time, add 70g of nitric acid with a mass fraction of 68% and 0.1g of copper nitrate catalyst. After stirring evenly, put the reactor into a 140℃ oil bath for heating. Control the pressure in the reactor to 4MPa(A). The reaction time is 3h. After the reaction is completed, reduce the reactor temperature to room temperature.

[0039] b. After releasing the pressure in the reactor, the liquid product in the reactor was transferred to a rotary evaporator and separated under reduced pressure at 33 KPa (A) and 120° C. to obtain a mixed organic acid product from which nitric acid and water were removed.

[0040] [Example 2]

[0041] a. Take 10g of a mixture of low-density polyethylene (LDPE) and polypropylene in a mass ratio of 1:1, add it to the reactor, add 0.5g of alumina catalyst, stir evenly, place the reactor in a 140℃ oil bath for heating, and continuously introduce NO into the autoclave. 2 , NO 2 The flow rate was 100 ml / min, the pressure in the reactor was controlled at 3 MPa (A), the reaction time was 3 h, and the reactor temperature was lowered to room temperature after the reaction was completed.

[0042] b. After releasing the pressure in the reactor, the liquid product in the reactor was transferred to a rotary evaporator and separated under reduced pressure at 33 KPa (A) and 120° C. to remove most of the water and obtain a mixed organic acid product.

[0043] [Example 3]

[0044] a. Take 10g of linear low-density polyethylene (LLDPE), add it to the reactor, add 0.3g of copper nitrate catalyst, stir evenly, put the reactor into a 140℃ oil bath for heating, and continuously pass O into the autoclave. 2 , O 2 The flow rate was 200 ml / min, the pressure in the reactor was controlled at 7 MPa (A), the reaction time was 6 h, and the reactor temperature was lowered to room temperature after the reaction was completed.

[0045] b. After releasing the pressure in the reactor, the liquid product in the reactor was transferred to a rotary evaporator and separated under reduced pressure at 33 KPa (A) and 120° C. to remove most of the water and obtain a mixed organic acid product.

[0046] [Examples 4-9 and Comparative Examples 1-4]

[0047] Examples 4-9 and Comparative Examples 1-4 were carried out in the same manner as Example 1, and the differences are shown in Table 1.

[0048] Table 1. Different reaction conditions in various embodiments and comparative examples

[0049]

[0050]

[0051] The yield of the mixed organic acid prepared in each embodiment and comparative example (the average mass of organic acid produced per 1g of plastic feed / g, where the organic acid includes monocarboxylic acid and dicarboxylic acid) and the mass proportion of dicarboxylic acids with different carbon numbers were analyzed by gas chromatography-mass spectrometry (GC-MS) and are summarized in Table 2.

[0052] Table 2. Yield of mixed organic acids and mass proportion of dicarboxylic acids with different carbon numbers

[0053]

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recovering mixed organic acids from waste polyolefin plastics, characterized in that: The following steps are involved: a. Mixing waste polyolefin plastics with an oxidant and a catalyst to cause an oxidation reaction; b. After the reaction is completed, the reaction product is separated by reduced pressure distillation to obtain a mixed organic carboxylic acid.

2. The method according to claim 1, characterized in that: The waste polyolefin plastic is polyethylene, polypropylene or a mixture thereof, preferably polyethylene; preferably, polyethylene is selected from one or more of HDPE, LDPE, LLDPE and UHMWPE; polypropylene is selected from one or more of homopolymer polypropylene or copolymer polypropylene.

3. The method according to claim 1, characterized in that In step a, the oxidant is selected from one or more of HNO3, N2O, NO, NO2, H2O2, O2, and O3; preferably, the mass ratio of the oxidant to the waste polyolefin plastic is 4:1-20:

1.

4. The method according to claim 1, characterized in that: The catalyst is one or more of copper nitrate, alumina, zeolite and SiO2; preferably, the amount of the catalyst added is 0.1%-10% of the mass of the waste polyolefin plastic, preferably 1%-5%.

5. The method according to claim 1, characterized in that: The reaction temperature of step a is 100-180° C., the reaction pressure is 3-10 MPa (A), and the reaction time is 1-10 h.

6. The method according to claim 1, characterized in that In step a, the oxidation reaction obtains a carboxyl-containing mixed organic matter, including one or more of succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid and other organic carboxylic acids.

7. The method according to claim 1, characterized in that The temperature of the reduced pressure distillation in step b is 110-160° C. and the pressure is 10-50 KPa(A).

8. The method according to claim 1, characterized in that Step a also includes a pretreatment operation: the waste polyolefin plastic is transported to a thermal cracking reaction unit, and a thermal cracking reaction is performed under an inert gas atmosphere to generate polyolefin wax.

9. The method according to claim 8, characterized in that The thermal cracking reaction temperature is 300-500°C, and the reaction residence time is 1-2h.

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