A method for preparing upgraded tar by co-pyrolysis of lignite and waste plastics

Abstract

The present invention discloses a method for preparing upgraded tar by co-pyrolysis of lignite and waste plastic (PE). The method comprises the following steps: pre-treating the raw materials lignite and waste plastic (PE), uniformly mixing a certain amount of the treated lignite with the waste plastic (PE) in a mass ratio of 7:3 to obtain a lignite / waste plastic (PE) mixed sample, and adding the sample to a fixed-bed pyrolysis reactor; heating the lignite / waste plastic (PE) mixed sample in the fixed-bed pyrolysis reactor to 440-540°C under an N2 atmosphere for pyrolysis reaction; after the reaction is completed, the gaseous product is passed into a spherical cold trap filled with n-hexane solvent, the spherical cold trap being immersed in an ice-salt bath at 0-5°C to capture the pyrolysis liquid product; filtering the obtained pyrolysis liquid product to remove impurities, and then rotary evaporating to remove the n-hexane solvent to obtain upgraded tar. This method not only achieves the synergy of the pyrolysis processes of the two, but also increases the PE content in the raw materials to 30%, and most importantly, improves the quality of the tar and pyrolysis gas.

Description

Technical Field

[0001] The invention belongs to the field of coal energy and the technical field of comprehensive utilization of solid waste, and in particular relates to a method for preparing tar by co-pyrolysis of lignite and waste plastics. Background Art

[0002] Lignite with a low degree of coalification suffers from defects such as high moisture content, low calorific value, and susceptibility to spontaneous combustion, which restrict its processing and utilization. The production of fuel oil from lignite requires high temperatures and demanding process conditions. Furthermore, the resulting coal tar is high in dust, oxygen, and heavy components, making subsequent tar processing difficult.

[0003] Plastics and plastic products are widely used in daily life. The primary plastic waste is polyolefins such as polyethylene and polypropylene. However, plastic recycling accounts for only 30% of plastic production, with the majority of waste plastics disposed of through traditional methods such as landfill and incineration. Thermochemical processes such as pyrolysis can address the pollution problem of waste plastics. However, producing fuel oil from pyrolysis alone has its limitations, including demanding reaction conditions, high energy consumption, and a high wax content in the resulting liquid fuel oil.

[0004] Co-pyrolysis of coal and waste plastics can improve the quality of coal products while processing plastic waste. However, there are the following problems in the process of co-pyrolysis of plastics and coal: (1) According to the different reaction temperatures, the coal pyrolysis temperature is divided into low-temperature pyrolysis of 300-600℃, medium-temperature pyrolysis of 600-800℃ and high-temperature pyrolysis above 900℃. Most co-pyrolysis reactions in the existing technology are above 600℃, and their main purpose is to obtain high-quality coke. The pyrolysis temperature of plastics is about 400℃, and the pyrolysis temperature of coal is above 600℃. Plastics are in a molten state during coal pyrolysis. Although the tar yield is increased, the quality of the tar is reduced; (2) Since the increase in plastic content affects the quality of coke, the amount of plastic added is generally controlled within 10%, which cannot achieve the goal of processing waste plastics and solving the problem of white pollution. Summary of the Invention

[0005] The purpose of the present invention is to address the current shortcomings of lignite pyrolysis alone, such as the quality of tar and the harsh reaction conditions of plastic pyrolysis. By combining "hydrogen-poor" lignite with "hydrogen-rich" waste plastic polyethylene (PE), a new method for preparing fuel oil by co-pyrolysis of lignite and waste plastic PE is proposed. This method solves the problem of tar quality degradation caused by different pyrolysis temperatures in the existing co-pyrolysis process of coal and waste plastic, and also solves the problem of low waste plastic addition and low processing volume.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a method for preparing upgraded tar by co-pyrolysis of lignite and waste plastic PE, comprising the following steps:

[0008] (1) The raw material lignite is dried in an oven at 106°C for 36 hours, crushed, screened, and dried again for later use. The particle size of the processed lignite is ≤0.075mm. The waste plastic PE is crushed, screened, and dried for 8 hours for later use. The particle size of the processed waste plastic PE is ≤0.075mm.

[0009] (2) A certain amount of treated lignite and waste plastic PE were uniformly mixed in a mass ratio of 7:3 to obtain a lignite / waste plastic PE mixed sample, which was then added to a fixed-bed pyrolysis reactor;

[0010] (3) Under N2 atmosphere, the lignite / waste plastic PE mixed sample in the fixed bed pyrolysis reactor is heated to 440-540°C for pyrolysis reaction. After the reaction is completed, the gaseous product is passed into a spherical cold trap filled with n-hexane solvent. The spherical cold trap is immersed in an ice-salt bath at 0-5°C to capture the pyrolysis liquid product; the tar is dissolved in n-hexane, and the tar and pyrolysis gas in the product can be separated by cooling in the spherical cold trap. N-hexane improves the capture capacity of tar and avoids obtaining coal tar at a lower temperature;

[0011] (4) The pyrolysis liquid product obtained in step (3) is filtered to remove impurities, and then the n-hexane solvent is removed by rotary evaporation to obtain upgraded tar.

[0012] Preferably, the lignite in step (1) is selected from oil-rich coal with a tar yield of 7% to 12%.

[0013] Preferably, the mixing method in step (2) is a mechanical mixing method.

[0014] Specifically, the pyrolysis treatment temperature in step (3) is 440-540°C, 440-450°C, 450-500°C, 450-540°C, 450°C, 500°C, etc., but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable, preferably 450°C.

[0015] Preferably, the pyrolysis time in step (3) is 30 to 40 min, 30 to 35 min, or 35 to 40 min.

[0016] Specifically, the liquid pyrolysis product in step (4) is filtered by a circulating water vacuum pump and then separated into the n-hexane solvent and the upgraded tar by a rotary evaporator.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention uses plastic waste PE and lignite as raw materials and carries out co-pyrolysis at low temperature, which not only achieves the synergy of the pyrolysis process of the two, but also increases the PE content in the raw materials to 30%, greatly increasing the use of waste plastics, solving the pollution problem caused by waste plastics to the environment, and reducing the use of fossil resources. Most importantly, it improves the product composition of the liquid tar from the pyrolysis of lignite, reduces the heavy components in the tar, reduces the oxygen content of the tar, improves the quality of the tar, reduces the content of H2O in the pyrolysis gas, increases the content of CO, and improves the quality of the pyrolysis gas;

[0019] (2) The entire process of the present invention is simple, has low energy consumption, is easy to operate, and has industrial application prospects;

[0020] (3) There is a synergistic effect in the co-pyrolysis process of lignite and plastic waste, which promotes the progress of the pyrolysis reaction and greatly improves the quality of the obtained oil products. It has an important theoretical basis and future application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a process flow chart for preparing upgraded tar by co-pyrolysis of lignite and waste plastics provided by the present invention. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0023] Example 1

[0024] like Figure 1 As shown, this embodiment provides a method for co-pyrolysis of lignite and waste plastics to prepare upgraded tar, which specifically includes the following steps:

[0025] (1) In this embodiment, Xinjiang Naomaohu lignite and waste PE are used as reaction raw materials. The raw lignite is dried in an oven at 106°C for 36 hours, crushed, screened, and dried again for use. The particle size of the treated lignite is ≤0.075 mm. The waste plastic PE is crushed, screened, and dried for 8 hours for use. The particle size of the treated waste plastic PE is ≤0.075 mm. The Xinjiang Naomaohu lignite and waste PE are fully mixed in a mass ratio of 7:3 by mechanical mixing to obtain a lignite / plastic PE mixed sample;

[0026] (2) adding the lignite / plastic mixed sample of step (1) into a fixed bed pyrolysis reactor, purging for 10 min under a nitrogen atmosphere at a constant flow rate of 120 mL / min, starting heating, raising the temperature to 450° C., and the reaction time for 30 min;

[0027] (3) After the reaction is completed, the solid product (semi-coke) remains in the reactor, and the gaseous product is passed into a spherical cold trap filled with 100 mL of n-hexane solvent. The spherical cold trap is placed in 0-5°C ice brine to capture the pyrolysis liquid product (tar), and the remaining pyrolysis gas overflows;

[0028] (4) The pyrolysis liquid product of step (3) is filtered using a circulating water vacuum pump, and then the n-hexane solvent is removed by a rotary evaporator to obtain pyrolysis light tar.

[0029] The tar produced by co-pyrolysis of Naomaohu lignite / PE waste plastics contains 45% more alkanes and olefins than the tar produced by pyrolysis of Naomaohu lignite alone, and the proportion of oxygen-containing products is reduced by 14%. The combination of Naomaohu lignite / PE effectively improves the quality of coal tar.

[0030] Example 2

[0031] The operating steps are the same as those in Example 1, except that the co-pyrolysis temperature of Naomaohu lignite and PE waste plastics is replaced from 450°C to 500°C.

[0032] Example 3

[0033] The operating steps are the same as those in Example 1, except that the waste plastic polyethylene PE is replaced with polypropylene PP.

[0034] Comparative Example 1

[0035] The operating steps are the same as those in Example 1, except that no PE waste plastic is added, and only Naomaohu lignite is pyrolyzed to obtain coal tar.

[0036] Comparative Example 2

[0037] The operating steps are the same as those in Example 2, except that no PE waste plastic is added, and only Naomaohu lignite is pyrolyzed to obtain coal tar.

[0038] The relative contents of alkanes and olefins in the GC / MS tars of Examples 1-3 and Comparative Examples 1-2 were calculated, and the results are shown in Table 1.

[0039] Table 1 Comparison of relative contents of alkanes and olefins in tars from Examples 1-3 and Comparative Examples 1-2 by GC / MS

[0040] Relative content of alkanes / % Relative content of olefins / % Total relative content of alkanes and alkenes / % Example 1 65.57 9.32 74.89 Example 2 31.82 10.47 42.29 Example 3 7.10 1.26 8.36 Comparative Example 1 23.90 6.38 30.28 Comparative Example 2 20.98 5.47 26.54

[0041] As shown in Table 1, the total relative content of alkanes and olefins in the tars obtained in Examples 1-2 was higher than that in Comparative Examples 1-2. Example 1, under optimal conditions, exhibited a 44.81% higher relative content of alkanes and olefins than Comparative Example 1. Under the same conditions, Example 3 exhibited a lower relative content of alkanes and olefins, 66.53% lower than that in Example 1. Therefore, the addition of PP waste plastics is detrimental to improving tar quality, while the addition of PE waste plastics significantly impacts tar composition. The method described in this invention improves the quality of coal tar compared to conventional methods.

[0042] The total relative content of oxygen-containing products of the GC / MS of the tar in Examples 1-3 and Comparative Examples 1-2 was calculated. The results are shown in Table 2.

[0043] Table 2 Comparison of the total relative content of oxygen-containing species in tars from Examples 1-3 and Comparative Examples 1-2 by GC / MS

[0044] Total relative content of oxygen-containing species / % Example 1 16.01 Example 2 21.49 Example 3 80.48 Comparative Example 1 29.58 Comparative Example 2 49.29

[0045] As shown in Table 2, the total relative content of oxygen-containing substances in the tar obtained in Examples 1-2 was lower than that in Comparative Examples 1-2. Example 2, which exhibited optimal conditions, was 27.8% lower than that in Comparative Example 2. The addition of PE waste plastic significantly impacted the composition of the tar, reducing the content of oxygen-containing substances in the coal tar and improving its quality. Under the same conditions, Example 3 exhibited a 50.9% higher relative content of oxygen-containing substances than Comparative Example 1. The addition of PP waste plastic increased the content of oxygen-containing substances in the coal tar, reducing its quality. Therefore, PP waste plastic is not suitable for treatment using this method.

[0046] The relative contents of the main components of the pyrolysis gas in Examples 1-3 and Comparative Examples 1-2 were calculated, and the results are shown in Table 3.

[0047] <![CDATA[CO2 / %]]> CO / % <![CDATA[H2O / %]]> <![CDATA[CH4 / %]]> <![CDATA[H2%]]> Example 1 0.65 50.61 3.33 16.99 28.42 Example 2 0 85.14 0 14.86 0 Example 3 20.43 7.76 22.53 45.44 3.83 Comparative Example 1 0.00 45.02 39.01 4.58 11.39 Comparative Example 2 20.40 19.21 31.03 12.93 16.43

[0048] As shown in Table 3, the relative water content in the pyrolysis gas obtained in Examples 1-3 is lower than that in Comparative Examples 1-2. Example 1 represents the optimal conditions, with the relative water content 35.68% lower than that in Comparative Example 1. Adding a small amount of PE waste plastic significantly reduces water production in the pyrolysis gas. Furthermore, the relative CO and H2 contents in the pyrolysis gas obtained in Examples 1-2 are higher than those in Comparative Examples 1-2. Adding a small amount of PE waste plastic promotes syngas production in the pyrolysis gas. The relative CO2 content in the pyrolysis gas obtained in Example 3 is higher than that in Example 1 and Comparative Example 1. Adding PP waste plastic promotes the production of the greenhouse gas CO2, which in turn reduces the quality of the pyrolysis gas.

[0049] The carbon content in the elemental analysis of the pyrolysis semi-coke in Examples 1-3 and Comparative Examples 1-2 was calculated, and the results are shown in Table 4.

[0050] C / ％ Example 1 79.42 Example 2 81.15 Example 3 82.75 Comparative Example 1 78.00 Comparative Example 2 79.48

[0051] As shown in Table 4, the carbon content of the pyrolysis semi-coke obtained in Examples 1-3 is higher than that in Comparative Examples 1-2. Example 3 is the optimal condition, which is 3.33% higher than the carbon content of the pyrolysis semi-coke in Comparative Example 1. The carbon content of the semi-coke can be increased by adding PE and PP waste plastics, thereby improving the quality of the pyrolysis semi-coke.

[0052] In summary, the above embodiments and comparative examples show that embodiment 1 is the optimal condition for the method of the present invention. The coal tar prepared by the method of the present invention contains higher alkanes and olefins, and less oxygen-containing substances, which improves the quality of the coal tar and has no adverse effects on pyrolysis gas and semi-coke. The method provided by the present invention for preparing upgraded tar by co-pyrolysis of lignite and waste plastics has a simple process flow and does not require the addition of a catalyst. The co-pyrolysis of lignite and waste plastics to prepare upgraded tar not only achieves clean and efficient utilization of coal, but also solves the problem of environmental pollution and converts plastic waste into resources.

[0053] The embodiments of the present invention are only used to illustrate the present invention and do not limit the scope of the claims. Other substantially equivalent alternatives that can be thought of by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for preparing upgraded tar by co-pyrolysis of lignite and waste plastic PE, characterized in that: The following steps are involved: (1) Xinjiang Naomaohu lignite and waste PE were used as reaction raw materials. The raw lignite was dried in an oven at 106°C for 36 hours, crushed, screened, and dried again for use. The particle size of the treated lignite was ≤0.075 mm. The waste plastic PE was crushed, screened, and dried for 8 hours for use. The particle size of the treated waste plastic PE was ≤0.075 mm. The Xinjiang Naomaohu lignite and waste PE were fully mixed at a mass ratio of 7:3 by mechanical mixing to obtain a lignite / plastic PE mixed sample. (2) adding the lignite / plastic mixed sample of step (1) into a fixed bed pyrolysis reactor, purging for 10 min under a nitrogen atmosphere at a constant flow rate of 120 mL / min, starting heating, raising the temperature to 450° C., and the reaction time for 30 min; (3) After the reaction is completed, the solid product remains in the reactor, and the gaseous product is passed into a spherical cold trap filled with 100 mL of n-hexane solvent. The spherical cold trap is placed in 0-5°C ice brine to capture the pyrolysis liquid product, and the remaining pyrolysis gas overflows; (4) filtering the pyrolysis liquid product of step (3) using a circulating water vacuum pump, and then removing the n-hexane solvent using a rotary evaporator to obtain pyrolysis light tar; The relative content of alkanes in tar is 65.57%, the relative content of olefins in tar is 9.32%, and oxygen-containing compounds account for 16.01%.

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