CN117186928A - Method for preparing long-chain alpha-olefin from polyethylene - Google Patents
Method for preparing long-chain alpha-olefin from polyethylene Download PDFInfo
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- -1 polyethylene Polymers 0.000 title claims abstract description 65
- 239000004711 α-olefin Substances 0.000 title claims abstract description 59
- 239000004698 Polyethylene Substances 0.000 title claims abstract description 57
- 229920000573 polyethylene Polymers 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims description 40
- 238000006243 chemical reaction Methods 0.000 claims abstract description 95
- 238000004227 thermal cracking Methods 0.000 claims abstract description 64
- 238000004519 manufacturing process Methods 0.000 claims abstract description 13
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 28
- 239000007788 liquid Substances 0.000 claims description 18
- 239000000203 mixture Substances 0.000 claims description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 17
- 229920001903 high density polyethylene Polymers 0.000 claims description 16
- 239000004700 high-density polyethylene Substances 0.000 claims description 16
- 229920001684 low density polyethylene Polymers 0.000 claims description 15
- 239000004702 low-density polyethylene Substances 0.000 claims description 15
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- 239000000463 material Substances 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 12
- 238000010791 quenching Methods 0.000 claims description 9
- 229920000092 linear low density polyethylene Polymers 0.000 claims description 8
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- 230000000171 quenching effect Effects 0.000 claims description 6
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- 238000001816 cooling Methods 0.000 claims description 3
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- 150000001336 alkenes Chemical class 0.000 abstract description 21
- 239000002994 raw material Substances 0.000 abstract description 16
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 abstract description 12
- 150000001335 aliphatic alkanes Chemical class 0.000 abstract description 10
- 239000002699 waste material Substances 0.000 abstract description 6
- 238000002360 preparation method Methods 0.000 abstract description 5
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- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 12
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- 239000004215 Carbon black (E152) Substances 0.000 description 5
- 239000003054 catalyst Substances 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- GGQQNYXPYWCUHG-RMTFUQJTSA-N (3e,6e)-deca-3,6-diene Chemical compound CCC\C=C\C\C=C\CC GGQQNYXPYWCUHG-RMTFUQJTSA-N 0.000 description 4
- 238000005160 1H NMR spectroscopy Methods 0.000 description 4
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- 239000008367 deionised water Substances 0.000 description 4
- 229910021641 deionized water Inorganic materials 0.000 description 4
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000006555 catalytic reaction Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000006356 dehydrogenation reaction Methods 0.000 description 3
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- 229920000098 polyolefin Polymers 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
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- VOITXYVAKOUIBA-UHFFFAOYSA-N triethylaluminium Chemical compound CC[Al](CC)CC VOITXYVAKOUIBA-UHFFFAOYSA-N 0.000 description 2
- CZGAOHSMVSIJJZ-UHFFFAOYSA-N 2,4-dimethyl-1-heptene Chemical group CCCC(C)CC(C)=C CZGAOHSMVSIJJZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
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- 229910052786 argon Inorganic materials 0.000 description 1
- 150000004945 aromatic hydrocarbons Chemical class 0.000 description 1
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- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 1
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
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- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
Abstract
The application relates to a method for producing and preparing long-chain alpha-olefin. Specifically, polyethylene is used as a raw material to carry out thermal cracking in a pressurized superheated steam environment of 0.2 to 2.0MPa (absolute pressure). The mixed system of polyethylene and pressurized superheated steam is quickly preheated to 450-550 ℃, then thermally cracked for 0.5-10 min, and the polyethylene is converted into long-chain alpha-olefin and other co-products (long-chain alkane, long-chain internal olefin and the like) with high efficiency. The yield of the C7-C30 long-chain alpha-olefin in the product can reach 30 percent. The application not only provides a new raw material route for the production and preparation of long-chain alpha-olefins, but also provides a way for the conversion of waste polyethylene into high-added-value long-chain alpha-olefins.
Description
Technical Field
The application relates to a production and preparation method of long-chain alpha-olefin, in particular to efficient conversion of polyethylene serving as a raw material to the long-chain alpha-olefin.
Background
The long-chain alpha-olefin has very wide application in the chemical synthesis field, and can be used as a raw material for synthesizing different kinds of chemicals. Depending on the carbon chain length, the field of application varies, for example, C4-C8 alpha-olefins are mainly used as ethylene and propylene comonomers; C12-C18 alpha-olefins are mainly used for the synthesis of detergents; C6-C20 alpha-olefins are used in synthetic lubricating oils; C6-C10 alpha-olefins are used as plasticizers.
At present, the mainstream preparation technology of long-chain alpha-olefin at home and abroad comprises a wax cracking method, an alkane dehydrogenation method and an ethylene oligomerization method.
The industrial alpha-olefins were first produced by wax cracking. Typical Chevron wax cracking schemes include vaporization, cracking, quenching, and separation. Because of the high wax content of Chinese crude oil, such as Daqing and Duchun crude oil, the wax content is up to 23% -25%, and the domestic alpha-olefin production is mainly wax cracking. Domestic wax cracking generally adopts wax with oil content of more than 30% as raw material, and is carried out under the conditions of low pressure, gas phase, high temperature and short residence time, and steam (water) is properly injected to improve the linear velocity so as to prevent coking in a tubular reactor. In order to improve the olefin yield, the single pass cracking rate of wax is usually controlled to be 25% -30%, and the energy consumption is increased due to the large-scale circulation of materials.
The dehydrogenation method of normal alkane is dominant by UOP company and is matched with alkylbenzene and fatty alcohol. The method comprises the steps of molecular sieve separation of normal alkane, dehydrogenation of normal alkane, rectification of alkylate and the like. The raw material linear alkane C10-C14 is separated from the straight-run kerosene/light diesel oil fraction, and the sulfur and nitrogen impurities of aromatic hydrocarbon are removed by hydrofining. The weakest link of the process is that the single pass conversion rate of normal alkane is only 11% -13%, resulting in higher product cost.
Ethylene oligomerization is currently the main production process for foreign alpha-olefins. The Shell, ineos, UOP, duPont, exxon, linde and Amoco companies with the technology are not assigned with the technology, and the domestic ethylene oligomerization technology is still in a development and perfection stage. Ethylene oligomerization process uses ethylene as raw material and prepares long-chain alpha-olefin through oligomerization under the action of catalyst. The catalyst may be classified into aluminum alkyl catalysis, nickel complex catalysis, zirconium catalysis, and the like. Among these, the aluminum alkyl catalytic process can be further divided into a one-step process and a two-step process. The one-step method uses triethylaluminum as a catalyst, ethylene is compressed and preheated to 23MPa and 180 ℃ and then is introduced into a reactor for oligomerization and displacement reaction, and the retention time is about 15min. The reaction product is recycled through separated ethylene, and after the reaction of the liquid phase product is stopped by NaOH aqueous solution, the liquid phase separation and rectification are carried out to obtain long chain alpha-olefin products with different carbon numbers. In the two-step method, triethylaluminum is used as a catalyst, and ethylene is compressed and preheated and then enters two reactors in parallel. The temperature of the first reactor is controlled between 160 and 275 ℃ and the pressure is between 10 and 25MPa, and long-chain alpha-olefins of C4 to C10 are mainly synthesized. In the second reactor, ethylene is chain-extended at 60-100deg.C and 10-20MPa, and then substitution reaction is performed at 245-300deg.C and 0.7-20.0MPa to produce long chain alpha-olefins of C12-C18. The reaction product is separated, recovered, recycled, rectified and the like to obtain long chain alpha-olefin products containing different carbon numbers. The ethylene oligomerization process has good product performance, but the catalyst of the process has high price, low catalytic activity and poor selectivity, and needs a large amount of cocatalysts and carriers. In addition, the process conditions are harsh, high temperature and high pressure are required, and the explosion hazard exists.
Thus, there is a need in the art for a process for preparing long chain alpha-olefins that is highly productive, simple to operate, environmentally friendly and safe.
Disclosure of Invention
The application aims to provide a method for efficiently converting long-chain alpha-olefin, which has high yield, simple and convenient operation, environmental protection and high safety.
In a first aspect of the present application, there is provided a process for preparing long chain alpha-olefins, the process comprising the steps of:
(s 1) providing a preheated gas-liquid mixture comprising molten polyethylene and water vapor; and
(s 2) carrying out thermal cracking reaction on the gas-liquid mixture under a pressurized environment to obtain long-chain alpha-olefin.
In another preferred example, the long chain alpha-olefin refers to a long chain alpha-olefin having 7 to 30 carbon atoms, preferably a long chain alpha-olefin of C7-C30.
In another preferred embodiment, the polyethylene is selected from the group consisting of: high density polyethylene, low density polyethylene, linear low density polyethylene, or a combination thereof.
In another preferred embodiment, the polyethylene has a weight average molecular weight of 2X 10 4 g/mol～30×10 4 g/mol, preferably 5X 10 4 g/mol～20×10 4 g/mol。
In another preferred embodiment, the polyethylene has a number average molecular weight of 1X 10 4 g/mol～10×10 4 g/mol, preferably 2X 10 4 g/mol～8×10 4 g/mol。
In another preferred embodiment, the polyethylene has a melting point of 100 to 200 ℃, preferably 100 to 180 ℃.
In another preferred embodiment, the polyethylene has a density of 0.75 to 1.0g/mL.
In another preferred example, the mass ratio of the polyethylene to the superheated steam is 10:1 to 1:10, preferably 5:1 to 1:5, for example 5:1, 2:1, 1:1.5, 1:2.
In another preferred embodiment, the method further comprises a pretreatment step with an inert gas purge. The inert gas is selected from one or more of nitrogen, argon and helium.
In another preferred embodiment, the gas-liquid mixture is preheated by (a) polyethylene and (b) water or steam.
In another preferred example, the preheating means preheating to 450 to 550 ℃, such as 485 ℃, 500 ℃, 515 ℃, 545 ℃.
In another preferred embodiment, the preheating is rapid preheating. Preferably at 20-50 deg.C/min.
In another preferred example, the gas-liquid mixture is a high-temperature gas-liquid mixture, and the temperature of the gas-liquid mixture is 450-550 ℃.
In another preferred example, the pressurized environment means that the pressure of the reaction system is controlled to be 0.2 to 2.0MPa (absolute pressure), for example, 0.5MPa, 1MPa, 1.5MPa.
In another preferred embodiment, the thermal cracking reaction is carried out at a temperature of 450 to 550 ℃, for example 485 ℃, 515 ℃, 545 ℃.
In another preferred embodiment, the thermal cracking reaction is carried out at a pre-heat temperature.
In another preferred embodiment, the method comprises the steps of:
and (3) mixing (a) polyethylene and (b) water or steam under a pressurized environment, quickly preheating to a set pyrolysis temperature, and continuing the reaction to carry out thermal cracking to obtain the long-chain alpha-olefin.
In another preferred embodiment, the reaction is carried out in a batch or continuous manner.
In another preferred example, when the reaction is performed in a batch manner, the reaction time of the thermal cracking reaction is 0.5 to 10min, for example, 0.5min, 1min, 3min, 5min, 10min.
In another preferred example, when the reaction is performed in a continuous manner, the reaction space time of the thermal cracking reaction is 0.5 to 10min, for example, 0.5min, 1min, 3min, 5min, 10min.
In another preferred embodiment, the reaction space time is defined as reaction space time = reactor volume/(feed mass flow/polyethylene density).
In another preferred embodiment, the reaction further comprises the step of quenching the reaction by rapid cooling.
In another preferred embodiment, when the reaction is performed in a batch mode, the reaction comprises: polyethylene and water are added, nitrogen purging is carried out for pretreatment, materials in the kettle are preheated to a preheating temperature (preferably 450-550 ℃), the system pressure is controlled to be 0.2-2.0 MPa (absolute pressure), and the reaction is continued for a period of time (0.5-10 min) after reaching a preset thermal cracking temperature, and rapid cooling and quenching thermal cracking are carried out.
In another preferred embodiment, when the reaction is performed in a continuous manner, the reaction comprises: the melted polyethylene and the superheated steam are mixed and enter a reaction tube, the temperature of thermal cracking is reached through rapid preheating, the pressure in a reaction system is controlled to be 0.2-2.0 MPa (absolute pressure), and then the product flows out of the reactor.
In a second aspect of the present application, there is provided an apparatus comprising a tubular reaction apparatus, a pressurizing apparatus and a thermocouple, the tubular reaction apparatus comprising a first temperature control zone for preheating and a second temperature control zone for conducting a thermal cracking reaction,
wherein the apparatus is configured to perform the method according to the first aspect of the application.
In another preferred embodiment, the inner diameter of the reaction tube of the tubular reaction device is 2cm, and the length of the tube is 400cm.
In another preferred embodiment, the device further comprises a heating device, optionally comprising a first heating device and a second heating device.
In another preferred embodiment, the first heating device is used for heating the first temperature control zone, and the second heating device is used for heating the second temperature control zone.
In another preferred embodiment, the thermocouple is a drawable thermocouple to determine the axial temperature distribution.
In another preferred example, the pressurizing means is configured to control the pressure to 0.2 to 2.0MPa (absolute pressure).
In another preferred embodiment, the heating device is configured to control the temperature at a pre-heating temperature.
It is understood that within the scope of the present application, the above-described technical features of the present application and technical features specifically described below (e.g., in the examples) may be combined with each other to constitute new or preferred technical solutions. And are limited to a space, and are not described in detail herein.
Detailed Description
The inventor of the application has found that, for the first time, polyethylene is used as a raw material, the polyethylene is placed in a pressurized superheated steam environment, and the mixed system is quickly preheated and thermally cracked for a period of time to complete the quick conversion of the polyethylene into long-chain alpha-olefins and co-products, wherein the yield of C7-C30 long-chain alpha-olefins can reach 30%, and the polyethylene can be highly selectively converted into C7-C30 long-chain alpha-olefins, and the percentage of the long-chain alpha-olefins in liquid olefins reaches about 70%. The method of the application prepares long-chain alpha-olefin by taking polyethylene as raw material, thereby not only providing an extra raw material route for the production and preparation of long-chain alpha-olefin, but also providing a way for converting waste polyethylene into high added value long-chain alpha-olefin. The present application has been completed on the basis of this finding.
Terminology
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
As used herein, the terms "comprising," "including," and "containing" are used interchangeably, and include not only closed-form definitions, but also semi-closed-form and open-form definitions. In other words, the term includes "consisting of … …", "consisting essentially of … …".
As used herein, when used in reference to a specifically recited value, the term "about" means that the value can vary no more than 1% from the recited value. For example, as used herein, the expression "about 100" includes 99 and 101 and all values therebetween (e.g., 99.1, 99.2, 99.3, 99.4, etc.).
As used herein, the term "internal olefin" refers to an olefin in which the carbon-carbon double bond is not at the end of the molecular chain.
The method of the application
Polyethylene is a thermoplastic resin made by polymerizing ethylene and may include high density polyethylene, low density polyethylene, linear low density polyethylene. Polyethylene is mainly used for manufacturing agricultural films, packaging films, wires and cables, pipes, hollow containers, coatings and the like. The global polyethylene productivity in 2020 reaches 1.27 hundred million tons. It is notable that polyethylene is not only one of the common plastics, but also an important constituent of waste plastics. Waste plastics have increased from 1.56 million tons in 2000 to 3.53 million tons in 2019 and have been handled up to 72% in landfills, severely damaging the natural environment.
Based on the method, the application provides a method for producing and preparing long-chain alpha-olefin by taking polyethylene as a raw material, which not only provides an extra raw material route for producing and preparing long-chain alpha-olefin, but also provides a way for converting waste polyethylene into high-added-value long-chain alpha-olefin.
Compared with the prior patent application of preparing liquid hydrocarbon products including gasoline and diesel oil by using polyolefin as raw material and adopting continuous thermal cracking method, the application can obtain long-chain alpha-olefin with high efficiency and high yield by using polyethylene as raw material.
And, in the continuous process of the present application, the tubular reaction apparatus includes a preheating section to preheat the reactants, after which the reactants enter a thermal cracking section, and heating is continued to maintain the reaction temperature, whereas in the prior patent application, the tubular reaction apparatus includes a preheating section to preheat the reactants, after which the reactants enter a adiabatic section, without external heat supply. In addition, parameters such as preheating temperature, reaction space time and the like are different from those of the prior patent application.
The method of the application comprises the following steps: the polyethylene is placed in a pressurized superheated steam environment, the mixed system is quickly preheated and thermally cracked for a certain time, and the polyethylene is subjected to high-efficiency conversion to long-chain alpha-olefins and other coproducts (long-chain alkanes, long-chain internal olefins and the like).
In the present application, yield of long chain α -olefins = liquid yield x olefin content in liquid x α -olefin fraction in olefin.
The liquid yield, the olefin content in the liquid and the alpha-olefin fraction in the olefin are complex functions of the preheat rate, the preheat temperature, the reaction time (space time), and all have a tendency to increase before decrease. Accordingly, there is a need for a preferred combination of operating processes to ensure yields of long chain alpha olefins.
Therefore, in order to improve the selectivity and yield of long chain alpha-olefins in the thermal cracking process of polyethylene, the present application makes preference for the type of polyethylene, the ratio of polyethylene and pressurized superheated steam, the pressure of the reaction system, the preheating rate of the thermal cracking system, the preheating temperature of the thermal cracking system, the time (space time) of the thermal cracking reaction, the product distribution of the thermal cracking reaction, the manner of the thermal cracking reaction, etc.:
preferably, the polyethylene is one or a mixture of high density polyethylene, low density polyethylene and linear low density polyethylene.
Preferably, the mass ratio of the polyethylene to the pressurized superheated steam is 10:1-1:2.
Preferably, the pressure of the thermal cracking reaction system is controlled to be 0.2-2.0 MPa (absolute pressure).
Preferably, the mixed system of the polyethylene and the pressurized superheated steam is preheated to a preheating temperature at 20-50 ℃/min.
Preferably, the mixed system of the polyethylene and the pressurized superheated steam is preheated to 450-550 ℃.
Preferably, the mixed system of the polyethylene and the pressurized superheated steam is preheated to the set pyrolysis temperature, and the time (space time) for continuous reaction is controlled to be 0.5-10 min.
Preferably, the polyethylene is thermally cracked in said pressurized superheated steam environment to produce C7-C30 long chain alpha-olefins, long chain alkanes and long chain internal olefins alike co-products.
Preferably, the conversion of polyethylene to long chain alpha-olefins and other co-products in the pressurized superheated steam environment is conducted in a batch or continuous manner.
The main advantages of the application include:
(1) The application not only provides a new raw material route for the production and preparation of long-chain alpha-olefins, but also provides a way for the conversion of waste polyethylene into high-added-value long-chain alpha-olefins.
(2) The method has the advantages of high yield of long-chain alpha-olefin, short reaction time, high production intensity of continuous reaction and low reaction space time.
The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. The experimental methods, in which specific conditions are not noted in the following examples, are generally conducted under conventional conditions or under conditions recommended by the manufacturer. Percentages and parts are weight percentages and parts unless otherwise indicated.
Example 1
Thermal cracking was performed in a batch mode using low density polyethylene and the difference between pressurized superheated steam and pressurized nitrogen was compared as the reaction medium.
The basic properties of a low density polyethylene pellet (manufacturer: chinese petrochemical) as a representative of the low density polyethylene are shown in table 1.
TABLE 1 basic Properties of Low Density polyethylene for testing
Batch thermal cracking
(1) The application relates to the pressurized superheated steam of the reaction medium
10g of low-density polyethylene and 2g of deionized water are initially added into a reaction kettle; the reaction kettle is closed after being purged by nitrogen; preheating the materials in the kettle from room temperature to 485 ℃ for about 16min. The system pressure is controlled to be 0.5MPa (absolute pressure) through a back pressure valve arranged at the rear part of the reaction kettle; and after reaching the preset thermal cracking temperature, continuing to react for 0.5, 3 or 5min, and quenching the thermal cracking by using a cold water bath to cool the reaction kettle.
(2) Conventional reaction medium pressurized nitrogen
10g of low-density polyethylene is initially added into a reaction kettle; the reaction kettle is purged by nitrogen and then filled with nitrogen with the pressure of 0.5MPa (absolute pressure); preheating the materials in the kettle from room temperature to 485 ℃ for about 17min. The system pressure is controlled to be 0.5MPa (absolute pressure) through a back pressure valve arranged at the rear part of the reaction kettle; and after reaching the preset thermal cracking temperature, continuing to react for 0.5, 3 or 5min, and quenching the thermal cracking by using a cold water bath to cool the reaction kettle.
Separation and analysis of products
The thermal cracking products are separated into wax, liquid products and gaseous products. Wherein the liquid product is defined as a hydrocarbon material dissolved in methylene chloride. The yields of wax and liquid product were determined by weighing and the gas yields were determined by normalization. The olefin content of the liquid product was determined by GC-MS and the ratio of the different types of olefins was determined by 1 H-NMR determination. The product distribution of thermal cracking of low density polyethylene for 0.5, 3 and 5min is shown in table 2.
Thermal cracking product distribution
TABLE 2 thermal cracking product distribution of Low Density polyethylene in pressurized superheated steam or Nitrogen
It can be seen that when nitrogen is used as the reaction medium, the majority of the olefins in the liquid are internal olefins and the yield of alpha-olefins is very low.
Example 2:
thermal cracking is carried out in a continuous manner using high density polyethylene.
As a representative of the high density polyethylene, a high density polyethylene pellet (manufacturer: duPont, U.S.) was used, the basic properties of which are shown in Table 3.
TABLE 3 basic Properties of high Density polyethylene for testing
Continuous thermal cracking
The thermal cracking of the high-density polyethylene is carried out by adopting a tubular reaction device with partition temperature control. The inner diameter of the reaction tube was 2cm, and the tube length was 400cm. A drawable thermocouple is mounted in the tube to determine the axial temperature distribution. The high-density polyethylene is preheated to be molten and mixed with superheated steam to enter a reaction tube, and the mass ratio of the high-density polyethylene to the water is controlled to be 2:1. The pressure in the reaction system was controlled to 1.0MPa (absolute pressure) by a back pressure valve. The molten high-density polyethylene and the superheated steam are preheated in a preheating section of the tubular reaction device, enter a thermal cracking section after being preheated to the preheating temperature, and continuously provide external heat in the thermal cracking section so as to maintain the temperature. The reaction space time of the materials in the isothermal zone (namely the thermal cracking section) at 500 ℃ is respectively controlled to be 1, 5 and 10 minutes by controlling the feeding mass flow and the heating power.
Separation and analysis of products
The thermally cracked product was quenched to 60 ℃ after exiting the reactor. The product is then separated into wax, liquid product and gaseous product. Wherein the liquid product is defined as a hydrocarbon material dissolved in methylene chloride. The yields of wax and liquid product were determined by weighing and the gas yields were determined by normalization. The olefin content of the liquid product was determined by GC-MS and the ratio of the different types of olefins was determined by 1 H-NMR determination. The product distribution is shown in Table 4 at reaction voids of 500℃in the thermal cracking reactor of 1, 5 and 10min, respectively.
Thermal cracking product distribution
TABLE 4 thermal cracking product distribution of high density polyethylene in pressurized superheated steam environment
It can be seen that the use of polyethylene in a continuous manner also produces high yields of alpha-olefins.
Example 3:
thermal cracking was performed in a batch mode using a polyolefin mixture, while comparing the effect of fast preheating (about 35 ℃/min) and slow preheating (about 15 ℃/min) on product distribution.
As a representative of the linear low density polyethylene, a certain linear low density polyethylene pellet (manufacturer: dow chemical) was used, and its basic properties are shown in Table 5. The low density polyethylene used in example 1 was taken as a representative of the low density polyethylene, and the high density polyethylene used in example 2 was taken as a representative of the high density polyethylene. The high-density polyethylene, the low-density polyethylene and the linear low-density polyethylene are mixed according to the mass ratio of 1:1:1 to form a polyethylene mixture.
TABLE 5 basic Properties of Linear Low Density polyethylene for testing
Fast preheating intermittent thermal cracking
10g of polyethylene mixture and 15g of deionized water are initially added into a reaction kettle; the reaction kettle is closed after being purged by nitrogen; preheating the materials in the kettle from room temperature to 485, 515 or 545 ℃ for about 13, 14 and 16 minutes respectively. The system pressure is controlled to be 1.5MPa (absolute pressure) through a back pressure valve arranged at the rear part of the reaction kettle; and after reaching the preset thermal cracking temperature, the reaction is continued for 1min, and then the reaction kettle is cooled by a cold water bath to quench thermal cracking.
Thermal cracking in a slow preheating batch mode
10g of polyethylene mixture and 15g of deionized water are initially added into a reaction kettle; the reaction kettle is closed after being purged by nitrogen; preheating the materials in the kettle from room temperature to 485, 515 or 545 ℃ for about 31, 33 and 35 minutes respectively. The system pressure is controlled to be 1.5MPa (absolute pressure) through a back pressure valve arranged at the rear part of the reaction kettle; and after reaching the preset thermal cracking temperature, the reaction is continued for 1min, and then the reaction kettle is cooled by a cold water bath to quench thermal cracking.
Separation and analysis of products
The thermal cracking products are separated into wax, liquid products and gaseous products. Wherein the liquid product is defined as a hydrocarbon material dissolved in methylene chloride. The yields of wax and liquid product were determined by weighing and the gas yields were determined by normalization. The olefin content of the liquid product was determined by GC-MS and the ratio of the different types of olefins was determined by 1 H-NMR determination. The product distribution at different preset thermal cracking temperatures is shown in table 6.
Polyethylene mixture product distribution
TABLE 6 thermal cracking product distribution of polyethylene mixtures in a pressurized superheated steam environment
It can be seen that the speed of preheating also has an effect on the product distribution. When the preheating rate is slower, the liquid yield decreases and the content of olefins in the liquid decreases, and a large amount of internal olefins are also present in the olefins in the liquid, resulting in a low overall α -olefin yield.
Example 4:
the thermal cracking is carried out in a batch mode using polypropylene.
As representative of polypropylene, a polypropylene particle (manufacturer: china petrochemical Co., ltd.) was used, and the basic properties thereof are shown in Table 7.
TABLE 7 basic Properties of polypropylene for testing
Batch thermal cracking
10g of polypropylene and 15g of deionized water are initially added into a reaction kettle; the reaction kettle is closed after being purged by nitrogen; preheating the materials in the kettle from room temperature to 485, 515 or 545 ℃ for about 13, 14 and 16 minutes respectively. The system pressure is controlled to be 1.5MPa (absolute pressure) through a back pressure valve arranged at the rear part of the reaction kettle; and after reaching the preset thermal cracking temperature, the reaction is continued for 1min, and then the reaction kettle is cooled by a cold water bath to quench thermal cracking.
Separation and analysis of products
The thermal cracking products are separated into wax, liquid products and gaseous products. Wherein the liquid product is defined as a hydrocarbon material dissolved in methylene chloride. The yields of wax and liquid product were determined by weighing and the gas yields were determined by normalization. The olefin content of the liquid product was determined by GC-MS and the ratio of the different types of olefins was determined by 1 H-NMR determination.
Polypropylene thermal cracking product distribution
For polypropylene feedstock, the yield of liquid product is maintained between 90-92% at each preset thermal cracking temperature. The highest content of the liquid product is 2, 4-dimethyl-1 heptene, and the yield can reach 7.11 percent. Others are complex mixtures of various C7-C30 alkanes and alkenes.
Although polyethylene and polypropylene are polyolefin, when polypropylene is used as a raw material, only various hydrocarbons having a high degree of branching can be obtained, and long chain α -olefins cannot be obtained with high selectivity.
All documents mentioned in this disclosure are incorporated by reference in this disclosure as if each were individually incorporated by reference. Further, it will be appreciated that various changes and modifications may be made by those skilled in the art after reading the above teachings, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.
Claims (10)
1. A process for preparing long chain α -olefins, said process comprising the steps of:
(s 1) providing a preheated gas-liquid mixture comprising molten polyethylene and water vapor; and
(s 2) carrying out thermal cracking reaction on the gas-liquid mixture under a pressurized environment to obtain long-chain alpha-olefin;
wherein, the preheating means preheating to 450-550 ℃.
2. The method of claim 1, wherein the polyethylene is selected from the group consisting of: high density polyethylene, low density polyethylene, linear low density polyethylene, or a combination thereof.
3. The method according to claim 1, wherein the mass ratio of polyethylene to steam is 10:1 to 1:10, preferably 5:1 to 1:5, such as 5:1, 2:1, 1:1.5, 1:2.
4. The method according to claim 1, wherein the preheating is performed at 20-50 ℃/min to 450-550 ℃.
5. The method according to claim 1, wherein the pressurized environment means that the pressure of the reaction system is controlled to be 0.2-2.0 MPa (absolute pressure), such as 0.5MPa, 1MPa, 1.5MPa.
6. The method of claim 1, wherein the thermal cracking reaction is carried out at 450-550 ℃, such as 485 ℃, 515 ℃, 545 ℃.
7. The method of claim 1, wherein the reaction is conducted in a batch or continuous mode.
8. The method according to claim 7, wherein the thermal cracking reaction has a reaction time of 0.5 to 10min, such as 0.5min, 1min, 3min, 5min, 10min, when the reaction is performed in a batch manner;
when the reaction is carried out in a continuous manner, the reaction space time of the thermal cracking reaction is 0.5 to 10min, for example, 0.5min, 1min, 3min, 5min, 10min.
9. The method of claim 7, wherein when the reaction is performed in a batch mode, the reaction comprises: adding polyethylene and water, blowing nitrogen to perform pretreatment, preheating materials in a kettle to a preheating temperature (preferably 450-550 ℃) at 20-50 ℃/min, controlling the system pressure to be 0.2-2.0 MPa (absolute pressure), continuing to react for a period of time (0.5-10 min) after reaching a preset thermal cracking temperature, and rapidly cooling and quenching the thermal cracking;
when the reaction is carried out in a continuous manner, the reaction comprises: the melted polyethylene and the superheated steam are mixed and enter a reaction tube, thermal cracking occurs after the mixture is preheated to the preheating temperature, the pressure in a reaction system is controlled to be 0.2-2.0 MPa (absolute pressure), and then the product flows out of the reactor.
10. An apparatus, characterized in that the apparatus comprises a tubular reaction device, a pressurizing device and a thermocouple, wherein the tubular reaction device comprises a first temperature control zone and a second temperature control zone, the first temperature control zone is used for preheating, the second temperature control zone is used for carrying out thermal cracking reaction,
wherein the apparatus is configured to perform the method of claim 1.
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