Method for preparing pentadiene from polyolefin and application

Abstract

The invention relates to the field of polyolefin, and discloses a method for preparing pentadiene from polyolefin, which comprises the following step: carrying out heat treatment on a mixture of water and polyolefin to obtain a pentadiene-containing product. Through the method, the product containing the pentadiene can be successfully prepared from the polyolefin, and the yield of the pentadiene in the heat treatment product containing the pentadiene is relatively high.

Description

Technical Field

[0001] The invention relates to the field of polyolefins, and in particular to a method and application of preparing pentadiene from polyolefins. Background Art

[0002] Plastic is one of the most widely used synthetic materials. Its production process is to convert fossil raw materials into small molecular monomers such as low-carbon olefins by chemical methods such as cracking, then polymerize the monomers into synthetic resins, and finally add additives to make plastics. The emergence of plastics has greatly facilitated people's lives, but the "white pollution" caused by discarded plastics has become a major problem facing mankind. It not only wastes resources, but also damages the environment and even threatens human health. Tiny plastic particles have been found in drinking water and in the bodies of marine animals. As of 2015, humans have produced approximately 6.3 billion tons of discarded plastics, of which only 9% have been recycled, 12% have been incinerated, and the remaining 79% have all been 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 misplaced resources. Turning waste into resources and changing "burden" into economic benefits is the only way to comprehensively utilize waste plastics. There are two major methods of plastic recycling: physical recycling and chemical recycling. Physical recycling generally involves simply cleaning and granulating waste plastics and then downgrading them to recycled plastics. As the number of recycling increases, the quality of recycled plastics gradually decreases until they are unusable. Chemical recycling is the process of converting waste plastics into valuable chemicals through chemical methods. Summary of the invention

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

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

[0007] The second aspect of the present invention provides the use of the above method in improving the yield of pentadiene in the process of producing pentadiene by heat treatment of polyolefin.

[0008] Through the above technical scheme, a product containing pentadiene can be successfully prepared from polyolefins, and the yield of pentadiene in the heat-treated product containing pentadiene is high, which can reach 40-60% by weight, the oil yield is also high, and the energy consumption is lower. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Description of Reference Numerals

[0011] 1. Pressurized mixing system; 2. Heat treatment reactor; 3. Separation system DETAILED DESCRIPTION

[0012] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0013] A 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 the present invention, there is no particular requirement for the conditions of heat treatment, but in a preferred embodiment of the present invention, the conditions of heat treatment include: a temperature of 360-460°C, which may be 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 range formed by any two of the above values ​​and a value within the range, and a pressure of not less than 12MPa, which may be 12MPa, 15MPa, 20MPa, 25MPa, 26MPa, 27MPa, 30MPa, 32MPa, 35MPa, 36MPa, 37MPa, 39MPa, 40MPa, 45MPa, 50MPa, 55MPa, 60MPa, 65MPa, 70MPa or a range formed by any two of the above values ​​and a value within the range. Unless otherwise specified, "pressure" in the present invention refers to gauge pressure.

[0015] In the present invention, the heat treatment conditions of the polyolefin and water are controlled within the above range, so that the polyolefin can be successfully dissolved in water and converted into oil, and more pentadiene can be obtained.

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

[0017] In the present invention, in order to obtain more pentadiene, the polyolefin is selected from at least one of polypropylene, polyethylene and polybutylene; or, the content of polypropylene in the polyolefin is not less than 80% by weight, and can be 80% by weight, 85% by weight, 90% by weight, 95% by weight, 100% by weight or a range formed by any two of the above values ​​and a value within the range. The method of the present invention is particularly suitable for polypropylene.

[0018] In the present invention, whether the polyolefin is newly prepared or recycled from waste plastics after being used for a period of time, more pentadiene can be obtained through the method of the present application.

[0019] In the present invention, the weight average molecular weight and / or number average molecular weight of the polyolefin is not limited, as long as pentadiene can be obtained after heat treatment. The method of the present invention is applicable to heat treatment of various common polyolefins to obtain pentadiene. In actual operation, the smaller the weight average molecular weight and / or number average molecular weight, the longer the treatment time, and the larger 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 1000, 10000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000, 2000000, 4000000, 6000000, 8000000, 10000000 or the range formed by any two of the above values, and the value within the range, is preferably 200000-600000.

[0020] In the present invention, in 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 temperature and time.

[0021] In the present invention, in order to obtain more pentadiene, the pressure of the heat treatment is preferably 12-60 MPa; preferably, the temperature of the heat treatment is 370-450°C; more preferably, the time of the heat treatment is 5-600 min, which can be 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 the range formed by any two of the above values, and the value within the range.

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

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

[0024] In the present invention, the method for separating pentadiene from the pentadiene-containing product is not limited, as long as pentadiene can be successfully separated, for example, distillation or extraction methods can be used.

[0025] Preferably, the water and polyolefin are mixed in a manner that: when the polyolefin is pressurized to 10-50% of the heat treatment pressure, the water is mixed with 10-50% of the weight of the polyolefin, and the mixture is further pressurized to not less than the heat treatment pressure and then mixed with the remaining water. In the present invention, the water and polyolefin are mixed in the manner described above, which can reduce 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 the present 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; further preferably, separation of pentadiene from the pentadiene-containing product is carried out in a separation system.

[0027] The second aspect of the present invention provides the use of the above method in improving the yield of pentadiene in the process of producing pentadiene by heat treatment of polyolefin.

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

[0029] Table 1

[0030] Polyolefins M Polypropylene powder 397084 Waste recycled polypropylene particles 310632 Polyethylene powder 151504

[0031] Oil yield test and calculation method: cool the reaction product to below 5°C, weigh and measure the weight of oil in the product, oil yield = weight of oil in the product / weight of plastic feed;

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

[0033] The coking yield test and calculation method is: weigh the weight of the solid residue obtained by filtering the product, coking yield = solid residue weight / plastic feed weight. 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] like Figure 1 As shown, the reactor is tubular, the screw extruder heats the polypropylene powder to a molten state, the screw extruder (pressurized mixing system 1) increases the pressure of the polyolefin to 10% of the pressure of the reactor heat treatment section, and water 10% of the weight of the polyolefin is added from the side line of the screw. After the screw continues to increase the pressure to the pressure of the heat treatment reactor 2, the above materials and the remaining water are sent to the heat treatment reactor 2, and the product is sent to the separation system 3 to separate pentadiene. The parameters of the heat treatment reactor and the product components are shown in Tables 2 and 3.

[0036] Table 2

[0037]

[0038]

[0039] Table 3

[0040]

[0041] Among them, the polypropylene powder in Example 6 was replaced with waste recycled polypropylene particles.

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

[0043] Example 12

[0044] The method of Example 1 is different in that 10% of the weight of water of the polypropylene is not added from the side line of the screw when the polypropylene pressure is increased to 10% of the pressure of the heat treatment reactor, but all the water is added to the heat treatment reactor when the polypropylene pressure is increased to the pressure of the heat treatment reactor. The results show that the energy consumption of the screw extruder of the method of Example 1 is reduced by 50% compared with that of this example, but the pentadiene yields of the two are similar.

[0045] It can be seen from the above results that the heat-treated product rich in pentadiene prepared by the method of the present invention has a higher yield of pentadiene, a higher oil yield, and lower energy consumption.

[0046] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing pentadiene from polyolefins, characterized in that: The method comprises: heat-treating a mixture of water and polyolefin to obtain a product containing pentadiene.

2. The method according to claim 1, wherein: The heat treatment conditions include: a temperature of 360-460°C and a pressure of not less than 12MPa; And / or, the weight ratio of water to polyolefin is 1-5:

1.

3. The method according to claim 1 or 2, wherein: The polyolefin is selected from at least one of polypropylene, polyethylene and polybutylene; Alternatively, the content of polypropylene in the polyolefin is not less than 80 wt%.

4. The method according to claim 1 or 2, wherein: The weight average molecular weight of the polyolefin is 1,000-10,000,000.

5. The method according to claim 1 or 2, wherein: The heat treatment pressure is 12-60MPa; And / or, the temperature of the heat treatment is 370-450°C; And / or, the heat treatment time is 5-600 min.

6. The method according to claim 5, wherein: The heat treatment pressure is 22-40MPa; And / or, the temperature of the heat treatment is 380-440°C; And / or, the heat treatment time is 10-240 min.

7. The method according to claim 1 or 2, wherein: The method further includes separating pentadiene from the pentadiene-containing product.

8. The method according to claim 1 or 2, wherein: The water and polyolefin are mixed in the following manner: when the polyolefin is pressurized to 10-50% of the heat treatment pressure, it is mixed with water which is 10-50% by weight of the polyolefin, and then the mixture is further pressurized to not less than the heat treatment pressure and then mixed with the remaining water.

9. The method according to claim 1 or 2, wherein: 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; Preferably, the heat treatment is carried out in a reactor; Preferably, separation of pentadiene from the pentadiene-containing product is carried out in a separation system.

10. Use of the method according to any one of claims 1 to 9 in improving the yield of pentadiene in a process for producing pentadiene by heat treatment of polyolefins.

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