Method and system for preparing alkyl alcohol by degrading polyolefin and application of method and system

Abstract

The invention relates to the technical field of polyolefin degradation, and provides a method and system for preparing alkyl alcohol through polyolefin degradation and application of the method and system. The method for preparing alkyl alcohol by degrading polyolefin comprises the following steps: mixing polyolefin powder, an ionic liquid catalyst, an initiator, trifluoroacetic acid and a solvent, heating to 70-110 DEG C, carrying out a coupling reaction, and contacting with water and a hydrolysis catalyst at 70-90 DEG C to carry out a hydrolysis reaction, thereby obtaining alkyl alcohol. According to the method and system for preparing alkyl alcohol through polyolefin degradation, the degradation temperature of polyolefin can be effectively reduced, the degradation efficiency is improved, the degradation time is shortened, a degradation product is converted into alkyl trifluoroacetate, alkyl trifluoroacetate is further hydrolyzed to generate alkyl alcohol with high economic value, the technological process is simple, and the method and system are suitable for industrial production. Complicated post-treatment procedures are not needed, the defects that a traditional polyolefin degradation method is high in reaction temperature, long in reaction time, low in product application value and the like are overcome, and the method has a good industrial prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of polyolefin degradation, and more specifically, to a method, system and application for preparing alkyl alcohols by polyolefin degradation. Background Art

[0002] Polyethylene and polypropylene are convenient and fast engineering synthetic plastics, which are widely used in plastic bags, plastic lunch boxes, food wraps, plastic films for agricultural use, etc. They are plastics with low toxicity and excellent environmental protection performance. However, there are huge challenges in the treatment of waste polyethylene or polypropylene. Currently, the effective methods are landfill, recycling and pelletizing, and incineration and pyrolysis. Waste polyolefin plastics are difficult to degrade. It takes 200 years to degrade in the ground, and a large amount of accumulation forms white garbage, seriously affecting the ecological environment; the recovery rate of recycling and pelletizing is low, and there are still a large number of untreated waste plastics; although incineration and pyrolysis can fundamentally reduce white pollution, it generates more waste gas, and the emissions of carbon, toxic and harmful gases and high energy consumption limit its development.

[0003] In recent years, the catalytic degradation of PE and PP plastics has received great attention. Existing polyolefin catalytic degradation technologies generally have problems such as high degradation temperature and low degradation efficiency, resulting in longer reaction time. CN113502174B discloses a noble metal-loaded inorganic solid acid catalyst for catalytic degradation of polyolefins. The degradation rate reaches 99% at 300 °C, and 80% of aviation oil products are recovered, but the catalyst and process costs are relatively high. CN105348557A discloses a method for degrading polyethylene to obtain polyethylene paraffin and liquid fuel by coupling alkane dehydrogenation and polyethylene metathesis reaction. The reaction temperature is 150 °C, and the reaction conditions are mild, but iridium and rhenium rare earth metals are used, and the price is relatively expensive, which limits its large-scale industrialization. CN115703900A discloses a method for photocatalytic degradation of polyolefins. Effective degradation of polyolefins is achieved under mild conditions by adding photocatalytic components to synergistically catalyze degradation with ionic liquids, but the degradation rate is slow, and the catalyst is greatly affected by the outside world.

[0004] Therefore, it is crucial to find and design a suitable reaction system and catalyst to achieve efficient degradation of polyolefins under mild conditions and recycle them in the form of high-value-added degradation products, which will gradually become the focus of research in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for preparing alkyl alcohols by polyolefin degradation, so as to solve the technical problems of high degradation temperature and low degradation efficiency commonly existing in the catalytic degradation of polyolefins in the prior art.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing alkyl alcohol by degrading polyolefin, comprising: mixing polyolefin powder, an ionic liquid catalyst, an initiator, trifluoroacetic acid and a solvent, heating to 70 - 110 °C for a coupling reaction, and then contacting with water and a hydrolysis catalyst at 70 - 90 °C for a hydrolysis reaction to obtain the alkyl alcohol.

[0008] In the present invention, the anion of the ionic liquid catalyst acts as a Lewis acid active center, which is activated by the initiator to form a tertiary carbocation and transfer hydrogen to the polyolefin chain, first realizing the cleavage of the polyolefin chain in the form of C3 - C7 olefins. Subsequently, under the synergistic catalysis of Bronsted acid (trifluoroacetic acid) and Lewis acid ionic liquid (ionic liquid catalyst), an addition esterification reaction occurs with trifluoroacetic acid to obtain an alkyl trifluoroacetate; then the alkyl trifluoroacetate contacts with water and a hydrolysis catalyst for a hydrolysis reaction to remove trifluoroacetic acid and obtain an alkyl alcohol. The trifluoroacetic acid removed by the hydrolysis reaction can be recycled to the coupling reaction, realizing the recycling of trifluoroacetic acid.

[0009] The method for preparing alkyl alcohol by degrading polyolefin provided by the present invention innovatively incorporates an esterification reaction, accelerating the forward progress of the polyolefin degradation reaction. Moreover, the hydrolysis equilibrium of the ester can inhibit the hydrolysis of trace water to the ionic liquid catalyst and prevent catalyst deactivation. In addition, the synergistic catalysis of Lewis acid ionic liquid (ionic liquid catalyst) and Bronsted acid (trifluoroacetic acid) accelerates both reactions simultaneously, enabling the efficient degradation of polyolefin under mild conditions.

[0010] The method for preparing alkyl alcohol by degrading polyolefin provided by the present invention can be carried out at a relatively low reaction temperature. It can not only effectively decompose polyolefin, but also convert the decomposition product into an alkyl trifluoroacetate. The alkyl trifluoroacetate is subsequently hydrolyzed to produce an alkyl alcohol, and the trifluoroacetic acid is recycled to the coupling reaction system. This technology achieves 100% atom economy; at the same time, it provides a new production method for alkyl alcohol, with advantages such as a simple process and high economic benefits.

[0011] In the present invention, too high reaction temperature will have an adverse effect on the ionic liquid catalyst.

[0012] According to some embodiments of the present invention, the ionic liquid catalyst comprises a halide complex of a nitrogen heterocyclic compound.

[0013] According to some embodiments of the present invention, the cation of the halide salt of the nitrogen heterocyclic compound is selected from at least one of 1 - methyl - 3 - butylimidazolium, 1 - butylpyridinium, 1 - butyl - 4 - dimethylaminopyridinium, 1 - butyl - tetramethylpyridinium, 1 - methyl - 3 - butylpyrimidinium; the anion of the halide salt of the nitrogen heterocyclic compound is [Al m Fe 2-m X n Y7-n - , where 0 ≤ m ≤ 2, 0 ≤ n ≤ 7, and X and Y are each independently selected from any one of fluoride ion, chloride ion, bromide ion, and iodide ion, preferably chloride ion and / or bromide ion.

[0014] According to some embodiments of the present invention, the initiator includes α-haloalcohol; preferably, the initiator is selected from at least one of 2-chloro-2-propanol, 2-bromo-2-propanol, 2-chloro-2-butanol, and 2-bromo-2-butanol.

[0015] In the present invention, using α-haloalcohol as the initiator can easily form a stable tertiary carbocation under the action of an ionic liquid catalyst, thereby reducing the activation energy of the degradation reaction and the reaction temperature. Moreover, the alkyl alcohol after activation does not need to be separated and can be recycled as the target product subsequently.

[0016] According to some embodiments of the present invention, the solvent includes dichloromethane.

[0017] According to some embodiments of the present invention, the hydrolysis catalyst includes an acidic ion exchange resin.

[0018] According to some embodiments of the present invention, the alkyl alcohol includes C 3 ~C 7 alkyl alcohol.

[0019] According to some embodiments of the present invention, the polyolefin includes at least one of polyethylene and polypropylene.

[0020] According to some embodiments of the present invention, the weight-average molecular weight of the polyolefin is 3000 to 30000.

[0021] According to some embodiments of the present invention, the mesh number of the polyolefin powder is 100 to 300 meshes.

[0022] According to some embodiments of the present invention, the mass ratio of the polyolefin to trifluoroacetic acid is 1:(1.1 to 2).

[0023] According to some embodiments of the present invention, the mass ratio of the ionic liquid catalyst to trifluoroacetic acid is 1:(1 to 4).

[0024] According to some embodiments of the present invention, the mass of the initiator is 1 to 5% of the mass of the ionic liquid catalyst.

[0025] According to some embodiments of the present invention, the mass ratio of the ionic liquid catalyst to the solvent is 1:(3 to 8).

[0026] ​According to some embodiments of the present invention, the reaction pressure of the coupling reaction is 0.2 to 0.5 MPa, and the reaction time is 2 to 8 h.

[0027] According to some embodiments of the present invention, the reaction pressure of the hydrolysis reaction is 0.1 to 0.3 MPa, and the space velocity is 0.5 to 3 h -1 , and the water-to-ester ratio is (2 to 6):1.

[0028] According to some embodiments of the present invention, the method includes:

[0029] S1. Mix polyolefin powder, ionic liquid catalyst, initiator, trifluoroacetic acid and solvent in a coupling reactor, and raise the temperature to 70 to 110 °C to carry out the coupling reaction;

[0030] S2. Separate the solid-liquid of the coupling reaction product, return the solid (uncompletely degraded polyolefin) to the coupling reactor; then layer the liquid, collect the upper-layer liquid, and return the lower-layer liquid (ionic liquid catalyst and trifluoroacetic acid) to the coupling reactor;

[0031] S3. Pass the upper-layer liquid into a reactive distillation column, contact it with water and hydrolysis catalyst at 70 to 90 °C, carry out hydrolysis reactive distillation to obtain the alkyl alcohol; collect trifluoroacetic acid at the top of the reactive distillation column and return it to the coupling reactor.

[0032] According to some embodiments of the present invention, the components returned to the coupling reactor are first dehydrated.

[0033] According to some embodiments of the present invention, the prepared alkyl alcohol is refined to obtain alkyl alcohol products with different chain lengths.

[0034] In a second aspect, the present invention provides a system for preparing alkyl alcohol by polyolefin degradation, including a coupling reactor, a separation and treatment unit, a hydrolysis raw material tank, a reactive distillation column, an optional dehydration and drying unit, and an optional refining unit;

[0035] Coupling reactor: used for carrying out a coupling reaction on a mixture including polyolefin powder, ionic liquid catalyst, initiator, trifluoroacetic acid and solvent to generate alkyl trifluoroacetate;

[0036] Separation and treatment unit: used for separating and treating the coupling reaction product to obtain alkyl trifluoroacetate, and returning the uncompletely degraded polyolefin, ionic liquid catalyst and trifluoroacetic acid to the coupling reactor;

[0037] Hydrolysis raw material tank: used for storing alkyl trifluoroacetate;

[0038] Reactive distillation column: It is used for the hydrolysis reactive distillation of alkyl trifluoroacetate in contact with water and a hydrolysis catalyst to produce the alkyl alcohol; and trifluoroacetic acid is collected at the top of the reactive distillation column and returned to the coupling reactor;

[0039] Dehydration and drying unit: It is used for dehydrating the components returned to the coupling reactor;

[0040] Refining unit: It is used for separating the alkyl alcohol to obtain alkyl alcohols with different chain lengths.

[0041] The system for preparing alkyl alcohol by polyolefin degradation provided by the present invention, through the cooperation of each unit, especially the separation and treatment unit utilizes the characteristics of immiscibility of different components due to polarity differences to separate them, greatly saving energy consumption and process flow.

[0042] In the present invention, the boiling point of trifluoroacetic acid is relatively low, and it is very easy to be separated from water and alkyl alcohol by distillation in the reactive distillation column and then return to the coupling reactor, avoiding cumbersome and complex post-treatment processes and devices.

[0043] In the third aspect, the present invention provides the application of the method described in the first aspect or the system described in the second aspect in the preparation of alkyl alcohol by polyolefin degradation.

[0044] The beneficial effects of the present invention are at least as follows:

[0045] The method and system for preparing alkyl alcohol by polyolefin degradation provided by the present invention can effectively reduce the degradation temperature of polyolefin, improve the degradation efficiency, shorten the degradation time, and convert the degradation products into alkyl trifluoroacetate, and then further hydrolyze to generate alkyl alcohol with high economic value. The process is simple and does not require complex post-treatment processes, overcoming the disadvantages of high reaction temperature, long reaction time, and low application value of products in traditional polyolefin degradation methods, and has good industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic production flow diagram for preparing alkyl alcohol by polyolefin degradation of the present invention.

[0047] Among them, A - coupling reactor, B - separation and treatment unit, C - hydrolysis raw material tank, D - reactive distillation column, E - dehydration and drying unit, F - refining unit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the following further describes the present invention in detail in conjunction with specific embodiments. It should be understood that the specific embodiments described here are only used to explain the patent in detail and do not limit the protection scope of the present invention in any way.

[0049] Combined withFigure 1 , the system for preparing alkyl alcohol by polyolefin degradation provided by the present invention is specifically described as follows:

[0050] The system for preparing alkyl alcohol by polyolefin degradation includes a coupling reactor, a separation and treatment unit, a hydrolysis raw material tank, a reactive distillation column, a dehydration and drying unit, and a refining unit.

[0051] The polyolefin is added to the coupling reactor after being cleaned, dried, and pulverized, and reacts with dichloromethane, trifluoroacetic acid, an initiator, and an ionic liquid catalyst. The discharged material is subjected to solid-liquid separation by the separation and treatment unit. Among them, the solid (incompletely degraded polyolefin) is returned to the coupling reactor, and the liquid is layered. The lower-layer catalyst and trifluoroacetic acid are returned to the coupling reactor; the upper-layer liquid is mainly a solution of trifluoroacetic acid alkyl ester, which enters the reactive distillation column through the hydrolysis raw material tank and contacts with water and a hydrolysis catalyst. Through the hydrolysis reaction, trifluoroacetic acid and alkyl alcohol are obtained. Trifluoroacetic acid is obtained from the top of the reactive distillation column and is recycled to the coupling reactor through the dehydration and drying unit. The C 3 ~C 7 aqueous solution of alkyl alcohol is taken out as a product and enters the refining unit for distillation separation as needed.

[0052] To illustrate the present invention more clearly, the present invention will be further described below with reference to embodiments.

[0053] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments, and equipment used in the following embodiments can all be obtained through market purchase or can be obtained by existing methods; the reagent dosages are all the dosages of reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0054] In the present invention:

[0055] (1) Polyolefin degradation rate (%) = (1 - mass of polyolefin after reaction / mass of polyolefin before reaction) × 100%;

[0056] (2)

[0057] (3)

[0058] In the above formula, n represents the number of alkyl groups.

[0059] Example 1

[0060] Adopt Figure 1According to the process shown below, a mixture of waste polyethylene powder (weight-average molecular weight of 5000, 150 mesh) with a mass ratio of 2:1:3:5:0.02, 1-methyl-3-butylimidazolium aluminum dichloride heptafluorate ionic liquid, trifluoroacetic acid, dichloromethane, and 2-chloro-2-propanol is mixed in a coupling reactor, heated to 75 °C, the pressure is controlled at 0.3 MPa, the reaction time is 3 h, the polyolefin degradation rate is 87%, and the yield of alkyl trifluoroacetate is 85%. The alkyl trifluoroacetate is introduced into a reactive distillation column to contact with water and an acidic ion exchange resin (German Lewatit S-100) to undergo a hydrolysis reaction. The temperature of the reactive distillation column is 80 °C, the pressure is 0.15 MPa, and the space velocity is 1 h -1 , and the water-to-ester ratio is 3:1, and the yield of alkyl alcohol is 98%.

[0061] Result: 0.83 kg (carbon-based) of alkyl alcohol can be produced from every 1 kg (carbon-based) of waste polyolefin raw material.

[0062] Examples 2 - 4

[0063] The methods of Examples 2 - 4 refer to Example 1, with the difference being the coupling reaction temperature. The results are as follows in the table:

[0064]

[0065]

[0066] Examples 5 - 7

[0067] The methods of Examples 5 - 7 refer to Example 1, with the difference being the ionic liquid catalyst. The results are as follows in the table:

[0068]

[0069] Example 8

[0070] Using Figure 1 According to the process shown below, a mixture of waste polypropylene powder (weight-average molecular weight of 25000, 200 mesh) with a mass ratio of 2:1:2.5:6:0.03, 1-butylpyridinium aluminum dichloride heptafluorate ionic liquid, trifluoroacetic acid, dichloromethane, and 2-chloro-2-butanol is mixed in a coupling reactor, heated to 105 °C, the pressure is controlled at 0.4 MPa, the reaction time is 3 h, the polyolefin degradation rate is 82%, and the yield of alkyl trifluoroacetate is 79%. The alkyl trifluoroacetate is introduced into a reactive distillation column to contact with water and an acidic ion exchange resin (German Lewatit S-100) to undergo a hydrolysis reaction. The temperature of the reactive distillation column is 85 °C, the pressure is 0.18 MPa, and the space velocity is 0.9 h -1 , and the water-to-ester ratio is 3.5:1, and the yield of alkyl alcohol is 98.4%.

[0071] Result: 0.78 kg (carbon basis) of alkyl alcohol can be produced from every 1 kg (carbon basis) of waste polyolefin raw material.

[0072] The higher the molecular weight of the polyolefin, the higher the degradation temperature is usually required to achieve relatively good degradation rate and degradation efficiency. In this example, the molecular weight of the polyolefin to be degraded is as high as 25,000, but both the polyolefin degradation rate and the amount of alkyl alcohol that can be produced from every 1 kg of polyolefin raw material are relatively high, indicating that the method and system for preparing alkyl alcohol by degrading polyolefin provided by this application also have good degradation effect when used to degrade polyolefins with higher molecular weight.

[0073] Example 9, Comparative Examples 1-3

[0074] The methods of Example 9 and Comparative Examples 1-3 refer to Example 1, with the difference being different initiators or no initiator added. The results are as follows in the table:

[0075]

[0076] Comparative Examples 4-6

[0077] The methods of Comparative Examples 4-6 refer to Example 1, with the difference being that other acids in equimolar amounts are used to replace trifluoroacetic acid or no trifluoroacetic acid is added. The results are as follows in the table:

[0078]

[0079]

[0080] Note: 1. The "alkyl ester yield" in the table represents the yield of alkyl acetate or alkyl trifluoroacetate or alkyl trichloroacetate.

[0081] 2. Due to the specific gravity being greater than water and being not suitable for separation from the top of the reactive distillation process of the present invention, trichloroacetic acid in Comparative Example 4 and acetic acid in Comparative Example 5 are separated by subsequent rectification.

[0082] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as specified, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for preparing alkyl alcohol by polyolefin degradation, characterized in that, comprising: Mixing polyolefin powder, ionic liquid catalyst, initiator, trifluoroacetic acid and solvent, heating to 70-110 °C for coupling reaction, and then contacting with water and hydrolysis catalyst at 70-90 °C for hydrolysis reaction to obtain the alkyl alcohol.

2. The method according to claim 1, characterized in that, The ionic liquid catalyst includes a halide salt complex of a nitrogen heterocyclic compound; preferably, the cation of the halide salt of the nitrogen heterocyclic compound is selected from at least one of 1-methyl-3-butylimidazolium, 1-butylpyridinium, 1-butyl-4-dimethylaminopyridinium, 1-butyl-tetramethylpyridinium, and 1-methyl-3-butylpyrimidinium; the anion of the halide salt of the nitrogen heterocyclic compound is [Al m Fe 2-m X n Y 7-n - , where 0 ≤ m ≤ 2, 0 ≤ n ≤ 7, X and Y are each independently selected from any one of fluoride ion, chloride ion, bromide ion, and iodide ion, preferably chloride ion and / or bromide ion;​ and / or, the initiator includes α-haloalcohol; preferably, the initiator is selected from at least one of 2-chloro-2-propanol, 2-bromo-2-propanol, 2-chloro-2-butanol, 2-bromo-2-butanol; and / or, the solvent includes dichloromethane; and / or, the hydrolysis catalyst includes acidic ion exchange resin.

3. The method according to claim 1 or 2, characterized in that, The alkyl alcohol includes C 3 to C 7 alkyl alcohol; and / or, the polyolefin includes at least one of polyethylene and polypropylene; and / or, the weight average molecular weight of the polyolefin is 3000-30000; and / or, the mesh number of the polyolefin powder is 100-300 mesh.

4. The method according to any one of claims 1-3, characterized in that, the mass ratio of the polyolefin to trifluoroacetic acid is 1:(1.1-2); and / or, the mass ratio of the ionic liquid catalyst to trifluoroacetic acid is 1:(1-4); and / or, the mass of the initiator is 1-5% of the mass of the ionic liquid catalyst; and / or, the mass ratio of the ionic liquid catalyst to the solvent is 1:(3-8).

5. The method according to any one of claims 1-4, characterized in that, the reaction pressure of the coupling reaction is 0.2-0.5 MPa, and the reaction time is 2-8 h.

6. The method according to any one of claims 1-5, characterized in that, The reaction pressure of the hydrolysis reaction is 0.1 to 0.3 MPa, and the space velocity is 0.5 to 3 h -1 , and the water-to-ester ratio is (2 to 6):

1.

7. The method according to any one of claims 1-6, characterized in that, the method comprises: S1. Mixing polyolefin powder, ionic liquid catalyst, initiator, trifluoroacetic acid and solvent in a coupling reactor, heating to 70-110 °C for coupling reaction; S2. Separating the solid-liquid of the coupling reaction product, returning the solid to the coupling reactor; then separating the liquid into layers, collecting the upper layer liquid, and returning the lower layer liquid to the coupling reactor; S3. Feeding the upper layer liquid into a reactive distillation column, contacting with water and hydrolysis catalyst at 70-90 °C for hydrolysis reactive distillation to obtain the alkyl alcohol; collecting trifluoroacetic acid at the top of the reactive distillation column and returning it to the coupling reactor.

8. The method according to claim 7, characterized in that, the components returned to the coupling reactor are first dehydrated; and / or, the prepared alkyl alcohol is refined to obtain alkyl alcohol products with different chain lengths.

9. A system for preparing alkyl alcohol by polyolefin degradation, characterized in that, comprising a coupling reactor, a separation and treatment unit, a hydrolysis raw material tank, a reactive distillation column, an optional dehydration and drying unit and an optional refining unit; Coupling reactor: used for coupling reaction of a mixture including polyolefin powder, ionic liquid catalyst, initiator, trifluoroacetic acid and solvent to generate alkyl trifluoroacetate; Separation and treatment unit: used for separating and treating the coupled reaction product to obtain alkyl trifluoroacetate, and returning the incompletely degraded polyolefin, ionic liquid catalyst and trifluoroacetic acid to the coupling reactor; Hydrolysis raw material tank: used for storing alkyl trifluoroacetate; Reactive distillation column: used for the hydrolysis reactive distillation of alkyl trifluoroacetate in contact with water and hydrolysis catalyst to prepare the alkyl alcohol; and collecting trifluoroacetic acid at the top of the reactive distillation column and returning it to the coupling reactor; Dehydration and drying unit: used for dehydrating the components returned to the coupling reactor; Purification unit: used for separating the alkyl alcohol to obtain alkyl alcohols with different chain lengths.

10. Use of the method according to any one of claims 1-8 or the system according to claim 9 in the preparation of alkyl alcohol by polyolefin degradation.

Images