Process for the preparation of pentadienes from polyolefins and applications

Abstract

The present application relates to the field of polyolefins, and discloses a method for preparing pentadiene from polyolefins, which comprises: subjecting a mixture of water and polyolefins to heat treatment to obtain a product containing pentadiene. Through the above method, the product containing pentadiene can be successfully prepared from polyolefins, and the yield of pentadiene in the heat-treated product containing pentadiene is relatively high.

Description

Methods and applications for preparing pentadiene from polyolefins Technical Field

[0001] This invention relates to the field of polyolefins, and more particularly to methods and applications for preparing pentadiene from polyolefins. Background Technology

[0002] Plastics are among the most widely used synthetic materials by humankind. Their production process involves using chemical methods such as pyrolysis to convert fossil fuels into small-molecule monomers such as low-carbon olefins. These monomers are then polymerized into synthetic resins, and finally, additives are added to create the final plastic. While plastics have greatly facilitated people's lives, the "white pollution" caused by discarded plastics has become a major problem for humanity. It not only wastes resources but also damages the environment and even threatens human health. Tiny plastic particles have already been found in drinking water and in the bodies of marine animals. As of 2015, humans had generated approximately 6.3 billion tons of waste plastic, of which only 9% was recycled, 12% was incinerated, and the remaining 79% was landfilled or flowed into the natural environment.

[0003] pentadiene is a raw material for the production of synthetic plastics and synthetic rubber.

[0004] Waste plastics are a resource in the wrong place. Turning waste into resource and transforming a "burden" into economic benefits is the only way to comprehensively utilize waste plastics. There are two main categories of plastic recycling methods: physical recycling and chemical recycling. Physical recycling generally involves simply washing and granulating waste plastics before using them as recycled plastics, but the quality gradually decreases with each recycling cycle until they are unusable. Chemical recycling, on the other hand, transforms waste plastics into valuable chemicals through chemical methods. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and to provide a method and application for preparing pentadiene from polyolefins.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing pentadiene from polyolefins, the method comprising: heat-treating a mixture of water and polyolefins to obtain a product containing pentadiene.

[0007] A second aspect of the present invention provides the application of the above-described method in improving the pentadiene yield in the process of producing pentadiene from polyolefins by heat treatment.

[0008] The above technical solution can successfully prepare pentadiene-containing products from polyolefins. The pentadiene yield in the heat-treated pentadiene-containing products is high, reaching 40-60% by weight, and the oil yield is also high, with lower energy consumption. Attached Figure Description

[0009] Figure 1 is a schematic diagram of the system of the present invention.

[0010] Explanation of reference numerals in the attached figures

[0011] 1. Pressurized mixing system; 2. Heat treatment reactor; 3. Separation system Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The first aspect of the present invention provides a method for preparing pentadiene from polyolefins, the method comprising: heat-treating a mixture of water and polyolefins to obtain a product containing pentadiene.

[0014] In this invention, there are no particular requirements for the heat treatment conditions. However, in a preferred embodiment, the heat treatment conditions include: a temperature of 360-460°C, which can be any two of the following values: 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 415°C, 420°C, 425°C, 430°C, 440°C, 450°C, 460°C, or a value within that range; and a pressure of not less than 12 MPa, which can be any two of the following values: 12 MPa, 15 MPa, 20 MPa, 25 MPa, 26 MPa, 27 MPa, 30 MPa, 32 MPa, 35 MPa, 36 MPa, 37 MPa, 39 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, or a value within that range. Unless otherwise stated, "pressure" in this invention refers to gauge pressure.

[0015] In this invention, controlling the heat treatment conditions of polyolefin and water within the above-mentioned range allows the polyolefin to be successfully dissolved in water and oiled, while also yielding more pentadiene.

[0016] In this invention, in order to obtain more pentadiene, the weight ratio of water to polyolefin is 1-5:1, which can be any two values ​​within the range of 1:1, 1:2, 1:3, 1:4, 1:5 or above.

[0017] In this invention, to obtain more pentadiene, the polyolefin is selected from at least one of polypropylene, polyethylene, and polybutene; or, the polypropylene content in the polyolefin is not less than 80% by weight, and can be any two of the following values: 80% by weight, 85% by weight, 90% by weight, 95% by weight, 100% by weight, or values ​​within that range. The method of this invention is particularly applicable to polypropylene.

[0018] In this invention, whether the polyolefin is newly prepared or recycled waste plastic obtained after a period of use, more pentadiene can be obtained through the method of this application.

[0019] In this invention, the weight-average molecular weight and / or number-average molecular weight of the polyolefin are not limited, as long as pentadiene can be obtained after heat treatment. The method of this invention is applicable to heat-treating various common polyolefins to obtain pentadiene. In practice, the lower the weight-average molecular weight and / or number-average molecular weight, the longer the treatment time; the higher the weight-average molecular weight and / or number-average molecular weight, the longer the treatment time. Preferably, the weight-average molecular weight of the polyolefin is 1000-10000000, which can be... The range formed by any two of the following values: 1000, 10000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000, 2000000, 4000000, 6000000, 8000000, 10000000, and the values ​​within that range, preferably 200000-600000.

[0020] In this invention, during the actual preparation process, the higher the weight-average molecular weight and number-average molecular weight, the more pentadiene can be obtained by using higher temperatures and times.

[0021] In this invention, to obtain more pentadiene, the heat treatment pressure is preferably 12-60 MPa; preferably, the heat treatment temperature is 370-450°C; more preferably, the heat treatment time is 5-600 min, which can be any two of the following values: 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 55 min, 60 min, 65 min, 70 min, 80 min, 90 min, 100 min, 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, 240 min, 250 min, 300 min, 350 min, 400 min, 450 min, 500 min, 550 min, 600 min, or any value within the range.

[0022] In this invention, in order to obtain more pentadiene, the heat treatment pressure is 22-40 MPa; preferably, the heat treatment temperature is 380-440 °C; more preferably, the heat treatment time is 10-240 min.

[0023] Preferably, the method further includes: separating pentadiene from the pentadiene-containing product.

[0024] In this invention, there are no restrictions on the method for separating pentadiene from the pentadiene-containing product, as long as pentadiene can be successfully separated. For example, distillation or extraction methods can be used.

[0025] Preferably, the mixing method of water and polyolefin includes: pressurizing the polyolefin to 10-50% of the heat treatment pressure, mixing it with 10-50% by weight of water, and then further pressurizing the mixture to at least the heat treatment pressure before mixing it with the remaining water. In this invention, using the above-described method to mix water and polyolefin reduces energy consumption by at least 50% compared to directly pressurizing the polyolefin to the heat treatment pressure and then mixing it with all the water.

[0026] In this invention, the method is carried out in a pressurized mixing system, a reactor, and a separation system; preferably, the mixing of water and polyolefin is carried out in a pressurized mixing system; more preferably, the heat treatment is carried out in a reactor; and even more preferably, the separation of pentadiene from the pentadiene-containing product is carried out in a separation system.

[0027] A second aspect of the present invention provides the application of the above-described method in improving the pentadiene yield in the process of producing pentadiene from polyolefins by heat treatment.

[0028] The present invention will be described in detail below through examples. The polyolefins and recycled polypropylene granules used in the following examples and comparative examples were purchased from Dongguan Fangsen Plastics Co., Ltd., and the polypropylene powder and polyethylene powder were prepared by the inventors in their laboratory to obtain new materials. Their GPC test results are shown in Table 1 (Mw is the weight-average molecular weight):

[0029] Table 1

[0030] Polyolefin Mw polypropylene powder 397084 waste recycled polypropylene granules 310632 polyethylene powder 151504 surface

[0031] Oil yield test and calculation method: The reaction product is cooled to below 5°C, and the weight of the oil in the product is weighed. Oil yield = weight of oil in product / weight of plastic feed.

[0032] Pentadiene yield testing and calculation method: Gas chromatography analysis of the pentadiene weight content in the product oil; pentadiene yield = pentadiene weight content × oil yield / plastic feed weight.

[0033] Coking yield test and calculation method: Weigh the solid residue obtained from the filtered product. Coking yield = weight of solid residue / weight of plastic feed. The lower the value, the lower the amount of coking produced during the heat treatment process.

[0034] Examples 1-11 and Comparative Example 1

[0035] As shown in Figure 1, the reactor is tubular. A screw extruder heats the polypropylene powder to a molten state. In the screw extruder (pressurized mixing system 1), the polyolefin pressure is increased to 10% of the pressure in the reactor's heat treatment section. Water, equal to 10% of the polyolefin's weight, is added through the screw side line. The screw continues to pressurize to the pressure of heat treatment reactor 2, and the above material, along with the remaining water, is fed into heat treatment reactor 2. The product is then sent to separation system 3 to separate pentadiene. The parameters of the heat treatment reactor and the product composition are shown in Tables 2 and 3.

[0036] Table 2

[0037]

[0038]

[0039] Table 3

[0040]

[0041] In Example 6, the polypropylene powder was replaced with recycled polypropylene granules.

[0042] In Example 7, the polypropylene powder was replaced with polyethylene powder.

[0043] Example 12

[0044] The method of Example 1 was followed, except that instead of adding 10% water by weight of the polypropylene from the screw side line when the polypropylene pressure was increased to 10% of the pressure of the heat treatment reactor, all the water was added to the heat treatment reactor at the same time the polypropylene pressure was increased to the pressure of the heat treatment reactor. Results showed that the method of Example 1 reduced the energy consumption of the screw extruder by 50% compared to this example, but the pentadiene yields were similar.

[0045] The results above show that the heat-treated product rich in pentadiene prepared by the method of the present invention has a high yield of pentadiene and a high oil yield, and also has lower energy consumption.

[0046] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing pentadiene from polyolefins, characterized in that, The method includes: heat-treating a mixture of water and polyolefin to obtain a pentadiene-containing product; the heat treatment temperature is 420-470℃; the polypropylene content in the polyolefin is not less than 80% by weight; the heat treatment conditions include: a pressure not less than 12MPa; separating pentadiene from the pentadiene-containing product; the mixing method of water and polyolefin includes: pressurizing the polyolefin to 10-50% of the heat treatment pressure, mixing it with 10-50% by weight of water, and then further pressurizing the mixture to not less than the heat treatment pressure before mixing it with the remaining water.

2. The method according to claim 1, wherein, The weight ratio of water to polyolefin is 1-5:

1.

3. The method according to claim 1, wherein, The polyolefin is selected from polypropylene.

4. The method according to claim 1, wherein, The weight-average molecular weight of the polyolefin is 1,000-1,000,000.

5. The method according to claim 1, wherein, The heat treatment pressure is 12-60 MPa; and / or the heat treatment time is 5-600 min.

6. The method according to claim 5, wherein, The heat treatment pressure is 22-40 MPa; and / or the heat treatment time is 10-240 min.

7. The method according to claim 1, wherein, The method is carried out in a pressurized mixing system, a reactor, and a separation system; the mixing of water and polyolefin is carried out in the pressurized mixing system; the heat treatment is carried out in the reactor; and the separation of pentadiene from the pentadiene-containing product is carried out in the separation system.

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